Magnetic resonance imaging coated assembly

ABSTRACT

An assembly for shielding an implanted medical device from the effects of high-frequency radiation and for emitting magnetic resonance signals during magnetic resonance imaging. The assembly includes an implanted medical device and a magnetic shield comprised of nanomagnetic material disposed between the medical device and the high-frequency radiation. In one embodiment, the magnetic resonance signals are detected by a receiver, which is thus able to locate the implanted medical device within a biological organism.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application is a continuation-in-part of applicants'co-pending patent application Ser. No. 10/384,288, which in turn is acontinuation of co-pending applications Ser. No. 10/324,773 (filed onDec. 18, 2002), Ser. No. 10/313,847 (filed on Dec. 7, 2002), Ser. No.10/303,264 (filed on Nov. 25,2002), Ser. No. 10/273,738 (filed on Oct.18, 2002), Ser. No. 10/260,247 (filed on Sep. 30, 2002), Ser. No.10/242,969 (filed on Sep. 13, 2002), Ser. No. 10/229,183 (filed on Aug.26, 2002), Ser. 10/090,553 (filed on Mar. 4, 2002), and 10/054,407(filed on Jan. 22, 2002, now U.S. Pat. No. 6,506,972).

FIELD OF THE INVENTION

[0002] An assembly for imaging an implanted medical device, wherein themedical device is shielded by nanomagnetic material which, in additionto shielding the medical device from high-frequency electromagneticradiation, emits high frequency electromagnetic radiation.

BACKGROUND OF THE INVENTION

[0003] Magnetic resonance imaging (“MRI”) has been developed as animaging technique adapted to obtain both images of anatomical featuresof human patients as well as some aspects of the functional activitiesand characteristics of biological tissue. These images have medicaldiagnostic value in determining the state of health of the tissueexamined. Unlike the situation with fluoroscopic imaging, a patientundergoing magnetic resonance imaging procedure may remain in theactive-imaging system for a significant amount of time, e.g. a half-houror more, without suffering any adverse effects.

[0004] In an MRI process, a patient is typically aligned to place theportion of the patient's anatomy to be examined in the imaging volume ofthe MRI apparatus. Such an MRI apparatus typically comprises a primarymagnet for supplying a constant magnetic field (B₀) which, byconvention, is along the z-axis and is substantially homogeneous overthe imaging volume and secondary magnets that can provide linearmagnetic field gradients along each of three principal Cartesian axes inspace (generally X, Y, and Z, or X₁, X₂ and X₃, respectively). As isknown to those skilled in the art, a magnetic field gradient (ΔB₀/ΔX₁)refers to the variation of the field with respect to each of the threeprincipal Cartesian axes, X₁. The MRI apparatus also comprises one ormore RF (radio frequency) coils which provide excitation and detectionof the MRI signal. Additionally, or alternatively, detection coils maybe designed into the distal end of a catheter to be inserted into apatient. When such catheters are employed, their proximal ends areconnected to the receiving signal input channel of the magneticresonance imaging device. The detected signal is transmitted along thelength of the catheter from the receiving antenna and/or receiving coilin the distal end to the MRI input channel connected at the proximalend. Other components of an MRI system are the programmable logic unitand the various software programs which the programmable logic unitexecutes. Construction of an image from the received signals isperformed by the software of the MRI system.

[0005] The insertion of metallic wires into a biological organism (suchas, e.g., catheters and guidewires) while the organism is in a magneticresonance imaging environment poses potentially deadly hazards to theorganism through excessive heating of the wires. In some studies,heating to a temperature in excess of 74 degrees Centigrade has createdsuch hazards; see, e.g., an article by M.K. Konings, et al., in“Catheters and Guidewires in Interventional MRI: Problems andSolutions”, MEDICA MUNDI 45/1 March 2001.

[0006] The Konings et al. article lists three ways in which conductorsmay heat up in such environments: 1) eddy currents, 2) induction loops,and 3) resonating RF transverse electromagnetic (TEM) waves along thelength of the conductors. It is disclosed in this article that: “Becauseof the risks associated with metal guidewires, and catheters with metalconductors, in the MRI environment, there is an urgent need for anon-metallic substitute, both for guidewires and for signal transfer.”The authors further propose the use of “. . . a full-glass guidewirewith a protective polymer coating . . . .”

[0007] However, the use of such “. . . full glass guidewire . . . ”presents its own problems. Many medical devices (such as, e.g., guideswires, stents, etc.) require some degree of strength and flexibilitythat is not afforded by glass guidewires and that typically require theuse of metal or metal alloys in the device. The implementation of glassguidewires, optical fibers, etc., solutions would require substantialretooling of the, for example, catheter manufacturing industry and isnot a suitable solution for other medical instruments that a physicianmay wish to employ, e.g. guidewires, stents, etc, during a medicalprocedure within an MRI system.

[0008] Compositions adapted to assist in visualizing medical devices inmagnetic resonance imaging are well known. Reference may be had, e.g.,to U.S. Pat. No. 6,361,759, the entire disclosure of which is herebyincorporated by reference into this specification. This patent describesand claims: “A coating for visualizing medical devices in magneticresonance imaging, comprising a complex of formula (III):P-X-J-L-M^(n+)(II), wherein P is a polymer, X is a surface functionalgroup selected from the group consisting of an amino group and acarboxyl group, L is a chelate, M is a paramagnetic ion, n is an integerthat is 2 or greater and J is the linker or spacer molecule and J is alactam.”

[0009] U.S. Pat. No. 4,731,239 discloses and claims: “A method fornuclear magnetic resonance (NMR) imaging of a patient comprising, priorto the NMR imaging of a patient, administering to said patientferromagnetic, paramagnetic or diamagnetic particles effective toenhance an NMR image.”

[0010] U.S. Pat. No. 4,989,608 discloses and claims: “A device which isspecifically useful during magnetic resonance imaging of body tissuecomprising: a flexible member of resinous material adapted to beinserted in the body tissue, the flexible member having ferromagneticparticles embedded therein at a concentration of about 0.001% to about10% by weight of the material wherein, under magnetic resonance imaging,the flexible member exhibits characteristics which differ substantiallyfrom characteristics of the body tissue so that the visibility of theflexible member under magnetic resonance imaging is substantiallyenhanced, resulting in the flexible member being distinguishable fromadjacent tissue as a dark area in brighter tissues and as a bright areain darker tissues, said member being free of elements which tend todegrade the overall quality of magnetic resonance images of the bodytissue.” At column 2 of this patent, it is disclosed that:“Ferromagnetic particles in general can cause magnetic field artifacts(MRI signal voids, with adjacent very bright signal bands, hereinaftercalled ‘imaging artifacts’ which are considerably larger than the sizeof the particle.” The entire disclosure of this patent is herebyincorporated by reference into this specification.

[0011] U.S. Pat. No. 5,154,179 discloses and claims: “1. A catheterwhich is specifically useful during a magnetic resonance imaging of bodytissue comprising: a contrast agent; a flexible tubular member having afirst lumen with an additional lumen positioned therein, the additionallumen retaining the contrast agent therein; the flexible tubular memberbeing made of resinous material and adapted to be inserted in the bodytissue, the flexible tubular member having ferromagnetic particlesembedded therein at a concentration of about 0.001% to about 10% byweight of the material wherein, under magnetic resonance imaging, theflexible member exhibits characteristics which differ substantially fromcharacteristics of the body tissue so that the visibility of theflexible member under magnetic resonance is substantially enhanced,resulting in the flexible member being distinguishable from adjacenttissue as a dark area in brighter tissues and as a bright area in darkertissues, said member being free of elements which tend to degrade theoverall quality of magnetic images of the body tissue.” In the device ofthis patent, a ferromagnetic material was extruded into plastic as theplastic was being extruded to form the flexible tubular member. Theentire disclosure of this United States patent is hereby incorporated byreference in to this specification.

[0012] U.S. Pat. No. 5,462,053 discloses and claims: “1. A contrastagent adapted for magnetic resonance imaging of a sample, said contrastagent comprising a suspension in a medium acceptable for magneticresonance imaging of (a) coated particles of a contrast agent possessingparamagnetic characteristics and (b) coated particles of a contrastagent possessing diamagnetic characteristics, each of said coatingsbeing selected from a group of materials which [I] renders said coatedparticles (a) and (b) substantially compatible with and substantiallybiologically and substantially chemically inert to each other and theenvironments to which said contrast agent is exposed during magneticresonance imaging and [III] which substantially stabilizes saidsuspension; the nature of each of said coatings and the relative amountsof (a) and (b) in said suspension being such that the positive magneticsusceptibility of (a) substantially offsets the negative magneticsusceptibility of (b) and the resulting suspension has substantiallyzero magnetic susceptibility and, when employed in magnetic resonanceimaging, results in the substantial elimination of imaging artifacts.”The entire disclosure of this United States patent is herebyincorporated by reference into this specification. In column 1 of thispatent, it is disclosed that: “It is well known to enhance NMR . . .images by . . . introducing into the sample to be imaged ferromagnetic,diamagnetic, or paramagnetic particles which shadow the image producedto intensity and contrast the image generated by the NMR sensitivenuclei. See, for example, the disclosures of U.S. Pat. Nos. 4,731,239;4,863,715; 4,749,560; 5,069,216; 5,055,288; 5,023,072; 4,951,674;4,827,945; and 4,770,183. . . . ”

[0013] U.S. Pat. No. 5,744,958 discloses and claims: “A magneticresonance imaging system, including: an imaging region and a means forgenerating a magnetic resonance image of a target object in the imagingregion, said magnetic resonance image including an image of the targetobject, wherein the means for generating the magnetic resonance imageincludes means for producing an RF field having an RF frequency in theimaging region; and an instrument for use with the target object in theimaging region, said instrument including: an electricallynon-conductive body, sized for use with the target object in the imagingregion; and an electrically conductive, ultra-thin coating on at leastpart of the body, the coating being sufficiently thick to cause theinstrument to be positively shown in the magnetic resonance image inresponse to presence of the instrument in the imaging region with thetarget object during generation of the magnetic resonance image, whereinthe coating consists of material having a skin depth with respect tosaid RF frequency and the coating has a thickness less than the skindepth.” At column 4 of this patent, it is disclosed that: “The presentinvention is based on the inventor's recognition that an electricallyconductive, ‘ultra-thin’ coating (a coating whose thickness is less thanor of the same order of magnitude as the coating's skin depth withrespect to its electrical and magnetic properties and the frequency ofthe RF field in an MRI system) on an instrument can cause the instrumentto create just enough artifact to be visible when imaged by an MRIsystem, but not so much artifact as to obscure or distort unacceptablythe magnetic resonance imaging of a target (e.g., human tissue) alsobeing imaged by the MRI system. In other words, the invention controlsthe artifact in such a way as to make the instrument visible but notappreciably distort the tissue structures being imaged by the MRI. Anultra-thin coating on an instrument embodying the invention typicallyhas a thickness of on the order of hundreds or thousands of Angstroms.”The entire disclosure of this United States patent is herebyincorporated by reference into this specification.

[0014] U.S. Pat. No. 6,203,777 describes and claims: “In a method ofcontrast enhanced nuclear magnetic resonance diagnostic imaging whichcomprises administering into the vascular system of a subject a contrastenhancing amount of a nuclear magnetic resonance imaging contrast agentand generating an image of said subject, the improvement comprisingadministering as said contrast agent composite particles comprising abiotolerable, biodegradable, non-immunogenic carbohydrate orcarbohydrate derivative matrix material containing magneticallyresponsive particles, said magnetically responsive particles being of amaterial having a Curie temperature and said composite particles beingno larger than one micrometer in size.” The entire disclosure of thisUnited States patent is hereby incorporated by reference into thisspecification.

[0015] United States published patent application 2002/0176822 disclosesand claims: “A magnetic resonance imaging system, comprising: a magneticresonance device for generating a magnetic resonance image of a targetobject in an imaging region; and an instrument for use with the targetobject in the imaging region, said instrument including a body sized foruse in the target object and a polymeric-paramagnetic ion complexcoating thereon in which said complex is represented by formula (I):P-X-L-M^(n+)(I) wherein P is a polymer, X is a surface functional group,L is a chelate, M is a paramagnetic ion and n is an integer that is 2 orgreater.” The entire disclosure of this United States patent applicationis hereby incorporated by reference into this specification.

[0016] None of the prior art compositions or coatings appear to beadapted to both facilitate MRI imaging while simultaneously protectingbiological tissue within a living organism from the adverse effects ofthe MRI electromagnetic wave. By way of illustration, some of theadverse effects include heating of tissue in contact with an implanted,conductive medical device, and voltages induced across tissue near orcontiguous with leads of implanted medical devices.

[0017] It is an object of this invention to provide an assembly forprotecting biological tissue from the adverse effects of heating duringMRI scanning while simultaneously facilitating MRI imaging.

SUMMARY OF THE INVENTION

[0018] In accordance with this invention, there is provided an assemblyfor shielding an implanted medical device from the effects ofhigh-frequency radiation and for emitting magnetic resonance signalsduring magnetic resonance imaging. The assembly includes an implantedmedical device and a magnetic shield comprised of nanomagnetic materialdisposed between the medical device and the high-frequency radiation. Inone embodiment, the magnetic resonance signals are detected by a remotereceiver, which is thus able to locate the implanted medical devicewithin a biological organism.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be more fully understood by referenceto the following detailed thereof, when read in conjunction with theattached drawings, wherein like reference numerals refer to likeelements, and wherein:

[0020]FIG. 1 is a schematic sectional view of a shielded implanteddevice comprised of one preferred conductor assembly of the invention;

[0021]FIG. 1A is a flow diagram of a preferred process of the invention;

[0022]FIG. 2 is an enlarged sectional view of a portion of the conductorassembly of FIG. 1;

[0023]FIG. 3 is a sectional view of another conductor assembly of thisinvention;

[0024]FIG. 4 is a schematic view of the conductor assembly of FIG. 2;

[0025]FIG. 5 is a sectional view of the conductor assembly of FIG. 2;

[0026]FIG. 6 is a schematic of another preferred shielded conductorassembly;

[0027]FIG. 7 is a schematic of yet another configuration of a shieldedconductor assembly;

[0028]FIGS. 8A, 8B, 8C, and 8D are schematic sectional views of asubstrate, such as one of the specific medical devices described in thisapplication, coated with nanomagnetic particulate matter on its exteriorsurface;

[0029]FIG. 9 is a schematic sectional view of an elongated cylinder,similar to the specific medical devices described in this application,coated with nanomagnetic particulate (the cylinder encloses a flexible,expandable helical member, which is also coated with nanomagneticparticulate material);

[0030]FIG. 10 is a flow diagram of a preferred process of the invention;

[0031]FIG. 11 is a schematic sectional view of a substrate, similar tothe specific medical devices described in this application, coated withtwo different populations of elongated nanomagnetic particulatematerial;

[0032]FIG. 12 is a schematic sectional view of an elongated cylinder,similar to the specific medical devices described in this application,coated with nanomagnetic particulate, wherein the cylinder includes achannel for active circulation of a heat dissipation fluid;

[0033]FIGS. 13A, 13B, and 13C are schematic views of an implantablecatheter coated with nanomagnetic particulate material;

[0034]FIGS. 14A through 14G are schematic views of an implantable,steerable catheter coated with nanomagnetic particulate material;

[0035]FIGS. 15A, 15B and 15C are schematic views of an implantableguidewire coated with nanomagnetic particulate material;

[0036]FIGS. 16A and 16B are schematic views of an implantable stentcoated with nanomagnetic particulate material;

[0037]FIG. 17 is a schematic view of a biopsy probe coated withnanomagnetic particulate material;

[0038]FIGS. 18A and 18B are schematic views of a tube of an endoscopecoated with nanomagnetic particulate material;

[0039]FIGS. 19A and 19B are schematics of one embodiment of themagnetically shielding assembly of this invention;

[0040]FIGS. 20A, 20B, 20C, 20D, 20E, and 20F are enlarged sectionalviews of a portion of a shielding assembly illustrating nonaligned andmagnetically aligned nanomagnetic liquid crystal materials in differentconfigurations;

[0041]FIG. 21 is a graph showing the relationship of the alignment ofthe nanomagnetic liquid crystal material of FIGS. 20A and 20B withmagnetic field strength;

[0042]FIG. 22 is a graph showing the relationship of the attenuationprovided by the shielding device of this invention as a function offrequency of the applied magnetic field;

[0043]FIG. 23 is a flow diagram of one preferred process for preparingthe nanomagnetic liquid crystal compositions of this invention;

[0044]FIG. 24 is a sectional view of a multiplayer structure comprisedof different nanomagnetic materials;

[0045]FIG. 25 is a sectional view of another multilayer structurecomprised of different nanomagnetic materials and an electricalinsulating layer.

[0046]FIGS. 26 through 31 are schematic views of multilayer structurescomprised of nanomagnetic material;

[0047]FIGS. 32-33 are schematic illustrations of means for determiningthe extent to which the temperature rises in a substrate when exposed toa strong magnetic field;

[0048]FIG. 34 is a graph showing the relationship of the temperaturedifferentials in a shielded conductor and a non-conductor when each ofthem are exposed to the same magnetic field;

[0049]FIGS. 35-36 are schematics of preferred magnetic shield assembliesof the invention;

[0050]FIG. 37 is a phase diagram of a preferred nanomagnetic material;

[0051]FIG. 38 is a schematic of the spacing between components of thenanomagnetic material of this invention;

[0052]FIG. 39 illustrates the springback properties of one coatedsubstrate of the invention;

[0053]FIGS. 40, 41, and 42 are graphs illustrating the relationship ofthe applied magnetic field to the measured magnetic field when thecoated substrate of the invention is used as a shield;

[0054]FIGS. 43-47 are graphs depicting the properties of certain films;

[0055]FIG. 48 is a schematic of a particular assembly comprised of alayer of nanomagnetic material;

[0056]FIG. 49 is a schematic diagram of a magnetic resonance imaging(MRI) assembly;

[0057]FIG. 50 is a sectional view of a shielded medical instrument that,when implanted, is adapted to produce minimal image artifacts from theelectromagnetic waves produced during MRI imaging;

[0058]FIGS. 51 and 52 are schematic representations of the effects of ahigh-frequency electromagnetic wave upon a particular substrate;

[0059]FIGS. 53 through 55 are schematic illustrations of severalshielded medical devices that may be used in the assembly of thisinvention; and

[0060]FIGS. 56A, 56B, and 56C are schematic illustrations of onepreferred process of the invention.

[0061] The present invention will be described in connection with apreferred embodiment, however, it will be understood that there is nointent to limit the invention to the embodiment described. On thecontrary, the intent is to cover all alternatives, modifications, andequivalents as may be included within the spirit and scope of theinvention as defined by the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062]FIG. 1 is a schematic sectional view of one preferred device 10that is implanted in a living biological organism (not shown). Device 10is comprised of a power source 12, a first conductor 14, a secondconductor 16, a first insulative shield 18 disposed about power source12, a second insulative shield 20 disposed about a load 22, a thirdinsulative shield 23 disposed about a first conductor 14, and a secondconductor 16, and a multiplicity of nanomagentic particles 24 disposedon said first insulative shield 18 said second insulative shield 20, andsaid third insulative shield 23.

[0063] In one embodiment, the device 10 is a an implantable device usedto monitor and maintain at least one physiologic function that iscapable of operating in the presence of damaging electromagneticinterference; see, e.g., United States published patent application U.S.2002/0038135, the entire disclosure of which is hereby incorporated byreference into this specification.

[0064] In one aspect of this embodiment, the device 10 is an implantablepacemaker. These pacemakers are well known to those skilled in the art.Reference may be had, e.g., to U.S. Pat. Nos. 5,697,959; 5,697,956(implantable stimulation device having means for optimizing currentdrain); U.S. Pat. No. 5,456,692 (method for non-invasively altering thefunction of an implanted pacemaker); U.S. Pat. No. 5,431,691 (system forrecording and displaying a sequential series of pacing events), U.S.Pat. No. 5,984,005 (multi-event bin heart rate histogram for use with animplantable pacemaker); U.S. Pat. Nos. 5,176,138; 5,003,975; 6,324,427;5,788,717; 5,417,718; 5,228,438; and the like. The entire disclosure ofeach of these United States patents is hereby incorporated by referenceinto this specification.

[0065] In the embodiment depicted in FIG. 1, the power source 12 is abattery 12 that is operatively connected to a controller 26. Controller26 is operatively connected to the load 22 and the switch 28. Dependingupon the information furnished to controller 26, it may deliver nocurrent, direct current, and/or current pulses to the load 22.

[0066] In one embodiment, not shown, some or all of the controller 26and/or the wires 30 and 32 are shielded from magnetic radiation. Inanother embodiment, not shown, one or more connections between thecontroller 26 and the switch 28 and/or the load 22 are made by wirelessmeans such as, e.g., telemetry means.

[0067] In one embodiment, the power source 12 provides a source ofalternating current. In another embodiment, the power source 12 inconjunction with the controller 26 provides pulsed direct current.

[0068] The load 22 may, e.g., be any of the implanted devices known tothose skilled in the art. Thus, e.g., as described hereinabove, the load22 may be a pacemaker. Thus, e.g., load 22 may be an artificial heart.Thus, e.g., load 22 may be a heart-massaging device. Thus, e.g., load 22may be a defibrillator.

[0069] The conductors 14 and 16 may comprise conductive material(s) thathave a resistivity at 20 degrees Centigrade of from about 1 to about 100microohm-centimeters. Thus, e.g., the conductive material(s) may besilver, copper, aluminum, alloys thereof, mixtures thereof, etc.

[0070] In one embodiment, the conductors 14 and 16 consist essentiallyof such conductive material. Thus, e.g., in one embodiment it ispreferred not to use, e.g., copper wire coated with enamel.

[0071] In the first step of one embodiment of the process of thisinvention, and referring to FIG. 1A and step 40, the conductive wires 14and 16 (see FIG. 1) are coated with electrically insulative material.Suitable insulative materials include nano-sized silicon dioxide,aluminum oxide, cerium oxide, yttrium-stabilized zirconia, siliconcarbide, silicon nitride, aluminum nitride, and the like. In general,these nano-sized particles will preferably have a particle sizedistribution such that at least about 90 weight percent of the particleshave a maximum dimension in the range of from about 10 to about 100nanometers.

[0072] The coated conductors 14 and 16 may be prepared by conventionalmeans such as, e.g., the process described in U.S. Pat. No. 5,540,959,the entire disclosure of which is hereby incorporated by reference intothis specification. This patent describes and claims a process forpreparing a coated substrate, comprising the steps of: (a) creating mistparticles from a liquid, wherein: said liquid is selected from the groupconsisting of a solution, a slurry, and mixtures thereof, said liquid iscomprised of solvent and from 0.1 to 75 grams of solid material perliter of solvent, at least 95 volume percent of said mist particles havea maximum dimension less than 100 microns, and said mist particles arecreated from said first liquid at a rate of from 0.1 to 30 millilitersof liquid per minute; (b) contacting said mist particles with a carriergas at a pressure of from 761 to 810 millimeters of mercury; (c)thereafter contacting said mist particles with alternating current radiofrequency energy with a frequency of at least 1 megahertz and a power ofat least 3 kilowatts while heating said mist particles to a temperatureof at least about 100 degrees centigrade, thereby producing a heatedvapor; (d) depositing said heated vapor onto a substrate, therebyproducing a coated substrate; and (e) subjecting said coated substrateto a temperature of from about 450 to about 1,400 degrees centigrade forat least about 10 minutes.

[0073] By way of further illustration, one may coat conductors 14 and 16by means of the processes disclosed in a text by D. Satas entitled“Coatings Technology Handbook” (Marcel Dekker, Inc., New York, N.Y.,1991). As is disclosed in such text, one may use cathodic arc plasmadeposition (see pages 229 et seq.), chemical vapor deposition (see pages257 et seq.), sol-gel coatings (see pages 655 et seq.), and the like.One may also use one or more of the processes disclosed in this book forpreparing other coated members such as, e.g., sheath 4034 (see FIGS. 35and 36).

[0074]FIG. 2 is a sectional view of the coated conductors 14/16 of thedevice of FIG. 1. Referring to FIG. 2, and in the preferred embodimentdepicted therein, it will be seen that conductors 14 and 16 areseparated by insulating material 42. In order to obtain the structuredepicted in FIG. 2, one may simultaneously coat conductors 14 and 16with the insulating material so that such insulators both coat theconductors 14 and 16 and fill in the distance between them withinsulation.

[0075] Referring again to FIG. 2, the insulating material 42 that isdisposed between conductors 14/16 may be the same as the insulatingmaterial 44/46 that is disposed above conductor 14 and below conductor16. Alternatively, and as dictated by the choice of processing steps andmaterials, the insulating material 42 may be different from theinsulating material 44 and/or the insulating material 46. Thus, step 48(see FIG. 1A) of the process describes disposing insulating materialbetween the coated conductors 14 and 16. This step may be donesimultaneously with step 40 (see FIG. 1A); and it may be donethereafter.

[0076] The insulating material 42, the insulating material 44, and theinsulating material 46 each generally has a resistivity of from about1×10⁹ to about 1×10¹³ ohm-centimeters.

[0077] Referring again to FIG. 1A, after the insulating material42/44/46 (see FIG. 2) has been deposited, and in one embodiment, thecoated conductor assembly is preferably heat treated in step 50. Thisheat treatment often is used in conjunction with coating processes inwhich the heat is required to bond the insulative material to theconductors 14/16 (see FIG. 2).

[0078] The heat-treatment step may be conducted after the deposition ofthe insulating material 42/44/46, or it may be conducted simultaneouslytherewith. In either event, and when it is used, it is preferred to heatthe coated conductors 14/16 (see FIG. 2) to a temperature of from about200 to about 600 degrees Centigrade for from about 1 minute to about 10minutes.

[0079] Referring again to FIG. 1A, and in step 52 of the process, afterthe coated conductors 14/16 (see FIG. 2) have been subjected to heattreatment step 50, they are allowed to cool to a temperature of fromabout 30 to about 100 degrees Centigrade over a period of time of fromabout 3 to about 15 minutes.

[0080] One need not invariably heat treat and/or cool. Thus, referringto FIG. 1A, one may immediately coat nanomagnetic particles onto to thecoated conductors 14/16 in step 54 either after step 48 and/or afterstep 50 and/or after step 52.

[0081] Referring again to FIG. 1A, in step 54, nanomagnetic materialsare coated onto the previously coated conductors 14 and 16. This is bestshown in FIG. 2, wherein the nanomagnetic particles are identified asparticles 24.

[0082] In general, and as is known to those skilled in the art,nanomagnetic material is magnetic material which has an average particlesize less than 100 nanometers and, preferably, in the range of fromabout 2 to 50 nanometers. Reference may be had, e.g., to U.S. Pat. No.5,889,091 (rotationally free nanomagnetic material), U.S. Pat. Nos.5,714,136; 5,667,924; and the like. The entire disclosure of each ofthese United States patents is hereby incorporated by reference intothis specification.

[0083] The nanomagnetic materials may be, e.g., nano-sized ferrites suchas, e.g., the nanomagnetic ferrites disclosed in U.S. Pat. No.5,213,851, the entire disclosure of which is hereby incorporated byreference into this specification. This patent claims a process forcoating a layer of ferritic material with a thickness of from about 0.1to about 500 microns onto a substrate at a deposition rate of from about0.01 to about 10 microns per minute per 35 square centimeters ofsubstrate surface, comprising the steps of: (a) providing a solutioncomprised of a first compound and a second compound, wherein said firstcompound is an iron compound and said second compound is selected fromthe group consisting of compounds of nickel, zinc, magnesium, strontium,barium, manganese, lithium, lanthanum, yttrium, scandium, samarium,europium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium,cerium, praseodymium, thulium, neodymium, gadolinium, aluminum, iridium,lead, chromium, gallium, indium, samarium, cobalt, titanium, andmixtures thereof, and wherein said solution is comprised of from about0.01 to about 1,000 grams of a mixture consisting essentially of saidcompounds per liter of said solution; (b) subjecting said solution toultrasonic sound waves at a frequency in excess of 20,000 hertz, and toan atmospheric pressure of at least about 600 millimeters of mercury,thereby causing said solution to form into an aerosol; (c) providing aradio frequency plasma reactor comprised of a top section, a bottomsection, and a radio-frequency coil; (d) generating a hot plasma gaswithin said radio frequency plasma reactor, thereby producing a plasmaregion; (e) providing a flame region disposed above said top section ofsaid radio frequency plasma reactor; (f) contacting said aerosol withsaid hot plasma gas within said plasma reactor while subjecting saidaerosol to an atmospheric pressure of at least about 600 millimeters ofmercury and to a radio frequency alternating current at a frequency offrom about 100 kilohertz to about 30 megahertz, thereby forming a vapor;(g) providing a substrate disposed above said flame region; and (h)contacting said vapor with said substrate, thereby forming said layer offerritic material.

[0084] By way of further illustration, one may use the techniquesdescribed in an article by M. DeMarco, X.W. Wang, et al. on “Mossbauerand magnetization studies of nickel ferrites” published in the Journalof Applied Physics 73(10), May 15, 1993, at pages 6287-6289.

[0085] In general, the thickness of the layer of nanomagnetic materialdeposited onto the coated conductors 14/16 is less than about 5 micronsand generally from about 0.1 to about 3 microns.

[0086] After the nanomagnetic material is coated in step 54 of FIG. 1A,the coated assembly may be optionally heat-treated in step 56. In thisoptional step 56, it is preferred to subject the coated conductors 14/16to a temperature of from about 200 to about 600 degrees Centigrade forfrom about 1 to about 10 minutes.

[0087] In one embodiment, illustrated in FIG. 3, one or more additionalinsulating layers 43 are coated onto the assembly depicted in FIG. 2, byone or more of the processes disclosed hereinabove. This is conducted inoptional step 58 (see FIG. 1A).

[0088]FIG. 4 is a partial schematic view of the assembly 11 of FIG. 2,illustrating the current flow in such assembly. Referring to FIG. 4, itwill be seen that current flows into conductor 14 in the direction ofarrow 60, and it flows out of conductor 16 in the direction of arrow 62.The net current flow through the assembly 11 is zero; and the netLorentz force in the assembly 11 is thus zero when placed in an externalmagnetic field (not shown). Consequently, even high current flows in theassembly 11 do not cause such assembly to move.

[0089] In the embodiment depicted in FIG. 4, conductors 14 and 16 aresubstantially parallel to each other. As will be apparent, without suchparallel orientation, there may be some net current and some net Lorentzeffect.

[0090] In the embodiment depicted in FIG. 4, and in one preferred aspectthereof, the conductors 14 and 16 preferably have the same diametersand/or the same compositions and/or the same length.

[0091] Referring again to FIG. 4, the nanomagnetic particles 24 arepresent in a density sufficient so as to provide shielding from magneticflux lines 64. Without wishing to be bound to any particular theory,applicant believes that the nanomagnetic particles 24 trap and pin themagnetic lines of flux 64.

[0092] In order to function optimally, the nanomagnetic particles 24have a specified magnetization. As is known to those skilled in the art,magnetization is the magnetic moment per unit volume of a substance.Reference may be had, e.g., to U.S. Pat. Nos. 4,169,998; 4,168,481;4,166,263; 5,260,132; 4,778,714; and the like. The entire disclosure ofeach of these United States patents is hereby incorporated by referenceinto this specification.

[0093] Referring again to FIG. 4, the layer of nanomagnetic particles 24preferably has a saturation magnetization, at 25 degrees Centigrade, offrom about 1 to about 36,000 Gauss, or higher. In one embodiment, thesaturation magnetization at room temperature of the nanomagneticparticles is from about 500 to about 10,000 Gauss. For a discussion ofthe saturation magnetization of various materials, reference may be had,e.g., to U.S. Pat. Nos. 4,705,613; 4,631,613; 5,543,070; 3,901,741(cobalt, samarium, and gadolinium alloys), and the like. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification. As will be apparent to thoseskilled in the art, especially upon studying the aforementioned patents,the saturation magnetization of thin films is often higher than thesaturation magnetization of bulk objects.

[0094] In one embodiment, it is preferred to utilize a thin film with athickness of less than about 2 microns and a saturation magnetization inexcess of 20,000 Gauss. The thickness of the layer of nanomagneticmaterial is measured from the bottom surface of the layer that containssuch material to the top surface of such layer that contains suchmaterial; and such bottom surface and/or such top surface may becontiguous with other layers of material (such as insulating material)that do not contain nanomagnetic particles.

[0095] Thus, e.g., one may make a thin film in accordance with theprocedure described at page 156 of Nature, Volume 407, Sep. 14, 2000,that describes a multilayer thin film that has a saturationmagnetization of 24,000 Gauss.

[0096] By the appropriate selection of nanomagnetic particles, and thethickness of the films deposited, one may obtain saturationmagnetizations of as high as at least about 36,000 Gauss.

[0097] In the preferred embodiment depicted in FIG. 4, the nanomagneticparticles 24 are disposed within an insulating matrix so that any heatproduced by such particles will be slowly dispersed within such matrix.Such matrix, as indicated hereinabove, may be made from ceria, calciumoxide, silica, alumina, and the like. In general, the insulatingmaterial 42 preferably has a thermal conductivity of less than about 20(calories-centimeters/square centimeters-degree second)×10,000. See,e.g., page E-6 of the 63^(rd) Edition of the “Handbook of Chemistry andPhysics” (CRC Press, Inc., Boca Raton, Fla., 1982).

[0098] The nanomagnetic materials 24 typically comprise one or more ofiron, cobalt, nickel, gadolinium, and samarium atoms. Thus, e.g.,typical nanomagnetic materials include alloys of iron and nickel(permalloy), cobalt, niobium, and zirconium (CNZ), iron, boron, andnitrogen, cobalt, iron, boron, and silica, iron, cobalt, boron, andfluoride, and the like. These and other materials are descried in a bookby J. Douglas Adam et al. entitled “Handbook of Thin Film Devices”(Academic Press, San Diego, Calif., 2000). Chapter 5 of this bookbeginning at page 185, describes “magnetic films for planar inductivecomponents and devices;” and Tables 5.1 and 5.2 in this chapter describemany magnetic materials.

[0099]FIG. 5 is a sectional view of the assembly 11 of FIG. 2. Thedevice of FIG. 5, and of the other Figures of this application, ispreferably substantially flexible. As used in this specification, theterm flexible refers to an assembly that can be bent to form a circlewith a radius of less than 2 centimeters without breaking. Put anotherway, the bend radius of the coated assembly 11 can be less than 2centimeters. Reference may be had, e.g., to U.S. Pat. Nos. 4,705,353;5,946,439; 5,315,365; 4,641,917; 5,913,005; and the like. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification.

[0100] In another embodiment, not shown, the shield is not flexible.Thus, in one aspect of this embodiment, the shield is a rigid, removablesheath that can be placed over an endoscope or a biopsy probe usedinter-operatively with magnetic resonance imaging.

[0101] In another embodiment of the invention, there is provided amagnetically shielded conductor assembly comprised of a conductor and afilm of nanomagnetic material disposed above said conductor. In thisembodiment, the conductor has a resistivity at 20 degrees Centigrade offrom about 1 to about 2,000 microohm-centimeters and is comprised of afirst surface exposed to electromagnetic radiation. In this embodiment,the film of nanomagnetic material has a thickness of from about 100nanometers to about 10 micrometers and a mass density of at least about1 gram per cubic centimeter, wherein the film of nanomagnetic materialis disposed above at least about 50 percent of said first surfaceexposed to electromagnetic radiation, and the film of nanomagneticmaterial has a saturation magnetization of from about 1 to about 36,000Gauss, a coercive force of from about 0.01 to about 5,000 Oersteds, arelative magnetic permeability of from about 1 to about 500,000, and amagnetic shielding factor of at least about 0.5. In this embodiment, thenanomagnetic material has an average particle size of less than about100 nanometers.

[0102] In one preferred embodiment of this invention, a film ofnanomagnetic particles is disposed above at least one surface of aconductor. Referring to FIG. 6, and in the schematic diagram depictedtherein, a source of electromagnetic radiation 100 emits radiation 102in the direction of film 104. Film 104 is disposed above conductor 106,i.e., it is disposed between conductor 106 and the electromagneticradiation 102.

[0103] The film 104 is adapted to reduce the magnetic field strength atpoint 110 relative to the field strength at point 108 (which is disposedless than 1 centimeter above film 104) by at least about 50 percent.Thus, if one were to measure the magnetic field strength at point 108,and thereafter measure the magnetic field strength at point 110 (whichis disposed less than 1 centimeter below film 104), the latter magneticfield strength would be no more than about 50 percent of the formermagnetic field strength. Put another way, the film 104 has a magneticshielding factor of at least about 0.5.

[0104] In one embodiment, the film 104 has a magnetic shielding factorof at least about 0.9, i.e., the magnetic field strength at point 110 isno greater than about 10 percent of the magnetic field strength at point108. Thus, e.g., the static magnetic field strength at point 108 can be,e.g., one Tesla, whereas the static magnetic field strength at point 110can be, e.g., 0.1 Tesla. Furthermore, the time-varying magnetic fieldstrength of 100 nilliTesla would be reduced to about 10 milliTesla ofthe time-varying field.

[0105] Referring again to FIG. 6, the nanomagnetic material 103 in film104 has a saturation magnetization of form about 1 to about 36,000Gauss. This property has been discussed elsewhere in this specification.In one embodiment, the nanomagnetic material 103 has a saturationmagnetization of from about 200 to about 26,000 Gauss.

[0106] The nanomagnetic material 103 in film 104 also has a coerciveforce of from about 0.01 to about 5,000 Oersteds. The term coerciveforce refers to the magnetic field, H, which must be applied to amagnetic material in a symmetrical, cyclically magnetized fashion, tomake the magnetic induction, B, vanish; this term often is referred toas magnetic coercive force. Reference may be had, e.g., to U.S. Pat.Nos. 4,061,824; 6,257,512; 5,967,223; 4,939,610; 4,741,953; and thelike. The entire disclosure of each of these United States patents ishereby incorporated by reference into this specification.

[0107] In one embodiment, the nanomagnetic material 103 has a coerciveforce of from about 0.01 to about 3,000 Oersteds. In yet anotherembodiment, the nanomagnetic material 103 has a coercive force of fromabout 0.1 to about 10 Oersted.

[0108] Referring again to FIG. 6, the nanomagnetic material 103 in film104 preferably has a relative magnetic permeability of from about 1 toabout 500,000; in one embodiment, such material 103 has a relativemagnetic permeability of from about 1.5 to about 260,000. As used inthis specification, the term relative magnetic permeability is equal toB/H, and is also equal to the slope of a section of the magnetizationcurve of the film. Reference may be had, e.g., to page 4-28 of E.U.Condon et al.'s “Handbook of Physics” (McGraw-Hill Book Company, Inc.,New York, 1958).

[0109] Reference also may be had to page 1399 of Sybil P. Parker's“McGraw-Hill Dictionary of Scientific and Technical Terms,” FourthEdition (McGraw Hill Book Company, New York, 1989). As is disclosed onpage 1399, permeability is “. . . a factor, characteristic of amaterial, that is proportional to the magnetic induction produced in amaterial divided by the magnetic field strength; it is a tensor whenthese quantities are not parallel . . . .” Relative permeability is thepermeability of the material divided by the permeability of free space.

[0110] Reference also may be had, e.g., to U.S. Pat. Nos. 6,181,232;5,581,224; 5,506,559; 4,246,586; 6,390,443; and the like. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification.

[0111] In one embodiment, the nanomagnetic material 103 in film 104 hasa relative magnetic permeability of from about 1.5 to about 2,000.

[0112] Referring again to FIG. 6, the nanomagnetic material 103 in film104 preferably has a mass density of at least about 0.001 grams percubic centimeter; in one embodiment, such mass density is at least about1 gram per cubic centimeter. As used in this specification, the termmass density refers to the mass of a give substance per unit volume.See, e.g., page 510 of the aforementioned “McGraw-Hill Dictionary ofScientific and Technical Terms.” In one embodiment, the film 104 has amass density of at least about 3 grams per cubic centimeter. In anotherembodiment, the nanomagnetic material 103 has a mass density of at leastabout 4 grams per cubic centimeter.

[0113] In the embodiment depicted in FIG. 6, the film 104 is disposedabove 100 percent of the surfaces 112, 114, 116, and 118 of theconductor 106. In the embodiment depicted in FIG. 2, by comparison, thenanomagnetic film is disposed around the conductor.

[0114] Yet another embodiment is depicted in FIG. 7. In the embodimentdepicted in FIG. 7, the film 104 is not disposed in front of eithersurface 114, or 116, or 118 of the conductor 106. Inasmuch as radiationis not directed towards these surfaces, this is possible.

[0115] What is essential in this embodiment, however, is that the film104 be interposed between the radiation 102 and surface 112. It ispreferred that film 104 be disposed above at least about 50 percent ofsurface 112. In one embodiment, film 104 is disposed above at leastabout 90 percent of surface 112.

[0116] Many implanted medical devices have been developed to helpmedical practitioners treat a variety of medical conditions byintroducing an implantable medical device, partly or completely,temporarily or permanently, into the esophagus, trachea, colon, biliarytract, urinary tract, vascular system or other location within a humanor veterinary patient. For example, many treatments of the vascularsystem entail the introduction of a device such as a guidewire,catheter, stent, arteriovenous shunt, angioplasty balloon, a cannula orthe like. Other examples of implantable medical devices include, e.g.,endoscopes, biopsy probes, wound drains, laparoscopic equipment,urethral inserts, and implants. Most such implantable medical devicesare made in whole or in part of metal, and are not part of an electricalcircuit.

[0117] When a patient with one of these implanted devices is subjectedto high intensity magnetic fields, such as during magnetic resonanceimaging (MRI), electrical currents are induced in the metallic portionsof the implanted devices. The electrical currents so induced oftencreate substantial amounts of heat. The heat can cause extensive damageto the tissue surrounding the implantable medical device.

[0118] Furthermore, when a patient with one of these implanted devicesundergoes magnetic resonance imaging (MRI), signal loss and disruptionof the diagnostic image often occur as a result of the presence of ametallic object, which causes a disruption of the local magnetic field.This disruption of the local magnetic field alters the relationshipbetween position and frequency, which are crucial for proper imagereconstruction. Therefore, patients with implantable medical devices aregenerally advised not to undergo MRI procedures. In many cases, thepresence of such a device is a strict contraindication for MRI (SeeShellock, F.G., Magnetic Resonance Procedures: Health Effects andSafety, 2001 Edition, CRC Press, Boca Raton, Fla.; also see Food andDrug Administration, Magnetic Resonance Diagnostic Device: PanelRecommendation and Report on Petitions for MR Reclassification, Federalregister, 1988, 53, 7575-7579). Any contraindication such as this,whether a strict or relative contraindication, is a serious problemsince it deprives the patient from undergoing an MRI examination, oreven using MRI to guide other therapies, such as proper placement ofdiagnostic and/or therapeutics devices including angioplasty balloons,radio frequency ablation catheters for treatment of cardiac arrythmias,sensors to assess the status of pharmacological treatment of tumors, orverification of proper placement of other permanently implanted medicaldevices. The rapidly growing capabilities and use of MRI in these andother areas prevent an increasingly large group of patients frombenefiting from this powerful diagnostic and intra-operative tool.

[0119] The use of implantable medical devices is well known in the priorart. Thus, e.g., U.S. Pat. No. 4,180,600 discloses and claims animplantable medical device comprising a shielded conductor wireconsisting of a conductive copper core and a magnetically soft alloymetallic sheath metallurgically secured to the conductive core, whereinthe sheath consists essentially of from 2 to 5 weight percent ofmolybdenum, from about 15 to about 23 weight percent of iron, and fromabout 75 to about 85 weight percent of nickel. Although the device ofthis patent does provide magnetic shielding, it still creates heat whenit interacts with strong magnetic fields, and it can still disrupt anddistort magnetic resonance images.

[0120] U.S. Pat. No. 5,817,017 discloses and claims an implantablemedical device having enhanced magnetic image visibility. The magneticimages are produced by known magnetic imaging techniques, such as MRI.The invention disclosed in the '017 patent is useful for modifyingconventional catheters, stents, guidewires and other implantabledevices, as well as interventional devices, such as for suturing,biopsy, which devices may be temporarily inserted into the body lumen ortissue; and it is also useful for permanently implantable devices. Theentire disclosure of this United States patent is hereby incorporated byreference into this specification.

[0121] In the process disclosed in the '017 patent, paramagnetic ionicparticles are fixedly incorporated and dispersed in selective portionsof an implantable medical device such as, e.g., a catheter. When thecatheter coated with paramagnetic ionic particles is inserted into apatient undergoing magnetic resonance imaging, the image signal producedby the catheter is of higher intensity. However, paramagnetic implants,although less susceptible to magnetization than ferromagnetic implants,can produce image artifacts in the presence of a strong magnetic field,such as that of a magnetic resonant imaging coil, due to eddy currentsgenerated in the implants by time-varying electromagnetic fields that,in turn, disrupt the local magnetic field and disrupt the image.

[0122] Any electrically conductive material, even a non-metallicmaterial (and even one not in an electrical circuit) will develop eddycurrents and thus produce electrical potential and thermal heating inthe presence of a time-varying electromagnetic field or a radiofrequency field.

[0123] Thus, there is a need to provide an implantable medical device,which is shielded from strong electromagnetic fields, which does notcreate large amounts of heat in the presence of such fields, and whichdoes not produce image artifacts when subjected to such fields. It isone object of the present invention to provide such a device, includinga shielding device that can be reversibly attached to an implantablemedical device.

[0124]FIGS. 8A, 8B, 8C, and 8D are schematic sectional views of asubstrate 201, which is preferably a part of an implantable medicaldevice.

[0125] Referring to FIG. 8A, it will be seen that substrate 201 iscoated with nanomagnetic particles 202 on the exterior surface 203 ofthe substrate.

[0126] Referring to FIG. 8B, and in the embodiment depicted therein, thesubstrate 201 is coated with nanomagnetic particulate 202 on both theexterior surface 203 and the interior surface 204.

[0127] Referring to FIG. 8C, and in the preferred embodiment depictedtherein, a layer of insulating material 205 separates substrate 201 andthe layer of nanomagnetic coating 202.

[0128] Referring to FIG. 8D, it will be seen that one or more layers ofinsulating material 205 separate the inside and outside surfaces ofsubstrate 201 from respective layers of nanomagnetic coating 202.

[0129]FIG. 9 is a schematic sectional view of a substrate 301 which ispart of an implantable medical device (not shown). Referring to FIG. 9,and in the embodiment depicted therein, it will be seen that substrate301 is coated with nanomagnetic material 302, which may differ fromnanomagnetic material 202 (see FIG. 8A).

[0130] In one embodiment, the substrate 301 is in the shape of acylinder, such as an enclosure for a medical catheter, stent, guidewire,and the like. In one aspect of this embodiment, the cylindricalsubstrate 301 encloses a helical member 303, which is also coated withnanomagnetic particulate material 302.

[0131] In another embodiment (not shown), the cylindrical substrate 301depicted in FIG. 9 is coated with multiple layers of nanomagneticmaterials. In one aspect of this embodiment, the multiple layers ofnanomagnetic particulate are insulated from each other. In anotheraspect of this embodiment, each of such multiple layers is comprised ofnanomagnetic particles of different sizes and/or densities and/orchemical densities. In one aspect of this embodiment, not shown, each ofsuch multiple layers may have different thickness. In another aspect ofthis embodiment, the frequency response and degree of shielding of eachsuch layer differ from that of one or more of the other such layers.

[0132]FIG. 10 is a flow diagram of a preferred process of the invention.In FIG. 1A, reference is made to one or more conductors as being thesubstrate(s); it is to be understood, however, that other substrate(s)material(s) and/or configurations also may be used.

[0133] In the first step of this process depicted in FIG. 10, step 240,the substrate 201 (see FIG. 8A) is coated with electrical insulativematerial. Suitable insulative materials include nano-sized silicondioxide, aluminum oxide, cerium oxide, yttrium-stabilized zirconium,silicon carbide, silicon nitride, aluminum nitride, and the like. Ingeneral, these nano-sized particles will have a particle distributionsuch that at least 90 weight percent of the particles have a dimensionin the range of from about 10 to about 100 nanometers.

[0134] The coated substrate 201 may be prepared by conventional meanssuch as, e.g., the process described in U.S. Pat. No. 5,540,959.

[0135] Referring again to FIGS. 8C and 8D, and by way of illustrationand not limitation, these Figures are sectional views of the coatedsubstrate 201. It will be seen that, in the embodiments depicted,insulating material 205 separates the substrate and the layer ofnanomagnetic material 202. In order to obtain the structure depicted inFIGS. 8C and 8D, one may first coat the substrate with insulatingmaterial 205, and then apply a coat of nanomagnetic material 202 on topof the insulating material 205; see, e.g., step 248 of FIG. 10.

[0136] The insulating material 205 that is disposed between substrate201 and the layer of nanomagnetic coating 202 preferably has anelectrical resistivity of from about 1×10⁹ to about 1×10¹³ohm-centimeter.

[0137] After the insulating material 205 has been deposited, and in onepreferred embodiment, the coated substrate is heat-treated in step 250of FIG. 10. The heat treatment often is preferably used in conjunctionwith coating processes in which heat is required to bond the insulativematerial to the substrate 201.

[0138] The heat-treatment step 250 may be conducted after the depositionof the insulating material 205, or it may be conducted simultaneouslytherewith. In either event, and when it is used, it is preferred to heatthe coated substrate 201 to a temperature of from about 200 to about 600degree Centigrade for about 1 minute to about 10 minutes.

[0139] Referring again to FIG. 10, and in step 252 of the process, afterthe coated substrate 201 has been subjected to heat treatment step 250,the substrate is allowed to cool to a temperature of from about 30 toabout 100 degree Centigrade over a period of time of from about 3 toabout 15 minutes.

[0140] One need not invariably heat-treat and/or cool. Thus, referringto FIG. 10, one may immediately coat nanomagnetic particulate onto thecoated substrate in step 254, after step 248 and/or after step 250and/or after step 252.

[0141] In step 254, nanomagnetic material(s) are coated onto thepreviously coated substrate 201. This is best shown in FIGS. 8C and 8D,wherein the nanomagnetic materials are identified as 202.

[0142] In general, the thickness of the layer of nanomagnetic materialdeposited onto the coated substrate 201 is from about 100 nanometers toabout 10 micrometers and, more preferably, from about 0.1 to 3 microns.

[0143] Referring again to FIG. 10, after the nanomagnetic material iscoated in step 254, the coated substrate may be heat-treated in step256. In this optional step 256, it is preferred to subject the coatedsubstrate 201 to a temperature of from about 200 to about 600 degreeCentigrade for from about 1 to about 10 minutes.

[0144] In one embodiment (not shown) additional insulating layers may becoated onto the substrate 201, by one or more of the processes disclosedhereinabove; see, e.g., optional step 258 of FIG. 10.

[0145] Without wishing to be bound to any particular theory, theapplicants believe that the nanomagnetic particles 202 trap and pinmagnetic lines of flux impinging on substrate 201, while at the sametime minimizing or eliminating the flow of electrical currents throughthe coating and/or substrate.

[0146] Referring again to FIGS. 8A, 8B, 8C, and 8D, the layer ofnanomagnetic particles 202 preferably has a saturation magnetization, at25 degree Centigrade, of from about 1 to about 36,000 Gauss. In oneembodiment, such saturation magnetization is from about 1 to about26,000 Gauss. In another embodiment, the saturation magnetization atroom temperature of the nanomagnetic particles is from about 500 toabout 10,000 Gauss.

[0147] In one embodiment, it is preferred to utilize a thin film with athickness of less than about 2 microns and a saturation magnetization inexcess of 20,000 Gauss. The thickness of the layer of nanomagneticmaterial is measured from the bottom surface of such layer that containssuch material to the top surface of such layer that contains suchmaterial; and such bottom surface and/or such top surface may becontiguous with other layers of material (such as insulating material)that do not contain nanomagnetic particles. Thus, e.g., one may make athin film in accordance with the procedure described at page 156 ofNature, Volume 407, Sep. 14, 2000, that describes a multiplayer thinfilm that has a saturation magnetization of 24,000 Gauss.

[0148] As will be apparent, even when the magnetic insulating propertiesof the assembly of this invention are not absolutely effective, theassembly still reduces the amount of electromagnetic energy that istransferred to the coated substrate, prevents the rapid dissipation ofheat to bodily tissue, and minimization of disruption to the magneticresonance image.

[0149]FIG. 11 is a schematic sectional view of a substrate 401, which ispart of an implantable medical device (not shown). Referring to FIG. 11,and in the preferred embodiment depicted therein, it will be seen thatsubstrate 401 is coated with a layer 404 of nanomagnetic material(s).The layer 404, in the embodiment depicted, is comprised of nanomagneticparticulate 405 and nanomagnetic particulate 406. Each of thenanomagnetic particulate 405 and nanomagnetic particulate 406 preferablyhas an elongated shape, with a length that is greater than its diameter.In one aspect of this embodiment, nanomagnetic particles 405 have adifferent size than nanomagnetic particles 406. In another aspect ofthis embodiment, nanomagnetic particles 405 have different magneticproperties than nanomagnetic particles 406.

[0150] Referring again to FIG. 11, and in the preferred embodimentdepicted therein, nanomagnetic particulate material 405 and nanomagneticparticulate material 406 are designed to respond to static ortime-varying electromagnetic fields or effects in a manner similar tothat of liquid crystal display (LCD) materials. More specifically, thesenanomagnetic particulate materials 405 and nanomagnetic particulatematerials 406 are designed to shift alignment and to effect switchingfrom a magnetic shielding orientation to a non-magnetic shieldingorientation. As will be apparent, the magnetic shield provided by layer404, can be turned “ON” and “OFF” upon demand. In yet another embodiment(not shown), the magnetic shield is turned on when heating of theshielded object is detected.

[0151] Reference may be had to an article by Neil Mathur et al. entitled“Mesoscopic Texture in Magnanites” (January, 2003, Physics Today) for adiscussion of the fact that “. . . in cetain oxides of manganese, aspectacularly diverse range of exotic electronic and magnetic phases cancoexist at different locations within a single crystal. This strikingbehavior arises in manganites because their magnetic, electronic, andcrystal structures interact strongly with one another. For example, aferromagnetic metal can coexist with an insulator in which theirelectrons and their spins adopt intricate patterns.”

[0152]FIG. 12 is a schematic sectional view of substrate 501, which ispart of an implantable medical device (not shown). Referring to FIG. 12,and to the embodiment depicted therein, it will be seen that substrate501 is coated with nanomagnetic particulate material 502 which maydiffer from particulate material 202 (see FIGS. 8A through 8D) and/orparticulate material 302 (see FIG. 9) and/or materials 405 or 406 (seeFIG. 11). In the embodiment depicted in FIG. 12, the substrate 501 maybe a cylinder, such as an enclosure for a catheter, medical stent,guidewire, and the like. The assembly depicted in FIG. 12 includes achannel 508 located on the periphery of the medical device. An activelycirculating, heat-dissipating fluid (not shown) can be pumped intochannel 508 through port 507, and exit channel 508 through port 509. Theheat-dissipation fluid (not shown) will draw heat to another region ofthe device, including regions located outside of the body where the heatcan be dissipated at a faster rate. In the embodiment depicted, theheat-dissipating fluid flows internally to the layer of nanomagneticparticles 502.

[0153] In another embodiment, not shown, the heat dissipating fluidflows externally to the layer of nanomagnetic particulate material 502.

[0154] In another embodiment (not shown), one or more additional polymerlayers (not shown) are coated on top of the layer of nanomagneticparticulate 502. In one aspect of this embodiment, a high thermalconductivity polymer layer is coated immediately over the layer ofnanomagnetic particulate 502; and a low thermal conductivity polymerlayer is coated over the high thermal conductivity polymer layer. It ispreferred that neither the high thermal conductivity polymer layer northe low thermal conductivity polymer layer be electrically ormagnetically conductive. In the event of the occurrence of “hot spots”on the surface of the medical device, heat from the localized “hotspots” will be conducted along the entire length of the device beforemoving radially outward through the insulating outer layer. Thus, heatis distributed more uniformly.

[0155] Many different devices advantageously incorporate thenanomagnetic film of this invention. In the following section of thespecification, various additional devices that incorporate such film aredescribed.

[0156] The disclosure in the following section of the specificationrelates generally to an implantable medical device that is immune orhardened to electromagnetic insult or interference. More particularly,the invention is directed to implantable medical devices that utilizeshielding to harden or make these devices immune from electromagneticinsult (i.e. minimize or eliminate the amount of electromagnetic energytransferred to the device), namely magnetic resonance imaging (MRI)insult.

[0157] Magnetic resonance imaging (MRI) has been developed as an imagingtechnique to obtain images of anatomical features of human patients aswell as some aspects of the functional activities of biological tissue;reference may be had, e.g., to John D. Enderle's “Introduction toBiomedical Engineering”, Academic Press, San Diego, Calif., 2000 and, inparticular, pages 783-841 thereof. Reference may also be had to JosephD. Bronzino's “The Biomedical Engineering Handbook”, CRC Press, BocaRaton, Fla., 1995, and in particular pages 1006-1045 thereof. Theseimages have medical diagnostic value in determining the state of thehealth of the tissue examined.

[0158] In an MRI process, a patient is typically aligned to place theportion of the patient's anatomy to be examined in the imaging volume ofthe MRI apparatus. Such a MRI apparatus typically comprises a primarymagnet for supplying a constant magnetic field, B₀, which is typicallyof from about 0.5 to about 10.0 Tesla, and by convention, is along thez-axis and is substantially homogenous over the imaging volume, andsecondary magnets that can provide magnetic field gradients along eachof the three principal Cartesian axis in space (generally x, y, and z orx₁, x₂, and X₃, respectively). A magnetic field gradient refers to thevariation of the field along the direction parallel to B₀ with respectto each of the three principal Cartesian Axis. The apparatus alsocomprises one or more radio frequency (RF) coils, which provideexcitation for and detection of the MRI signal. The RF excitation signalis an electromagnetic wave with an electrical field E and magnetic fieldB₁, and is typically transmitted at frequencies of 3-100 negahertz.

[0159] The use of the MRI process with patients who have implantedmedical assist devices, such as guidewires, catheters, or stents, oftenpresents problems. These implantable devices are sensitive to a varietyof forms of electromagnetic interference (EMI), because theaforementioned devices contain metallic parts that can receive energyfrom the very intensive EMI fields used in magnetic resonance imaging.The above-mentioned devices may also contain sensing and logic andcontrol systems that respond to low-level electrical signals emanatingfrom the monitored tissue region of the patient. Since these implanteddevices are responsive to changes in local electromagnetic fields, theimplanted devices are vulnerable to sources of electromagnetic noise.The implanted devices interact with the time-varying radio-frequency(RF) magnetic field (B₁), which are emitted during the MRI procedure.This interaction can result in damage to the implantable device, or itcan result in heating of the device, which in turn can harm the patientor physician using the device. This interaction can also result indegradation of the quality of the image obtained by the MRI process.

[0160] Signal loss and disruption of a magnetic resonance image can becaused by disruption of the local magnetic field, which perturbs therelationship between position and image, which are crucial for properimage reconstruction. More specifically, the spatial encoding of the MRIsignal provided by the linear magnetic field can be disrupted, makingimage reconstruction difficult or impossible. The relative amount ofartifact seen on an MR image due to signal disruption is dependent uponsuch factors as the magnetic susceptibility of the materials used in theimplantable medical device, as well as the shape, orientation, andposition of the medical device within the body of the patient, which isvery often difficult to control.

[0161] All non-permanently magnetized materials have non-zero magneticsusceptibilities and are to some extent magnetic. Materials withpositive magnetic susceptibilities less than approximately 0.01 arereferred to as paramagnetic and are not overly responsive to an appliedmagnetic field. They are often considered non-magnetic. Materials withmagnetic susceptibilities greater than 0.01 are referred to asferromagnetic. These materials can respond very strongly to an appliedmagnetic field and are also referred as soft magnets as their propertiesdo not manifest until exposed to an external magnetic field.

[0162] Paramagnetic materials (e.g. titanium), are frequently used toencapsulate and shield and protect implantable medical devices due totheir low magnetic susceptibilities. These enclosures operate bydeflecting electromagnetic fields. However, although paramagneticmaterials are less susceptible to magnetization than ferromagneticmaterials, they can also produce image artifacts due to eddy currentsgenerated in the implanted medical device by externally applied magneticfields, such as the radio frequency fields used in the MRI procedures.These eddy currents produce localized magnetic fields, which disrupt anddistort the magnetic resonance image. Furthermore, the implanted medicaldevice shape, orientation, and position within the body make itdifficult to control image distortion due to eddy currents induced bythe RF fields during MRI procedures. Also, since the paramagneticmaterials are electrically conductive, the eddy currents produced inthem can result in ohmic heating and injury to the patient. The voltagesinduced in the paramagnetic materials can also damage the medicaldevice, by adversely interacting with the operation of the device.Typical adverse effects can include improper stimulation of internaltissues and organs, damage to the medical device (melting of implantablecatheters while in the MRI coil have been reported in the literature),and/or injury to the patient.

[0163] Thus, it is desirable to provide protection againstelectromagnetic interference, and to also provide fail-safe protectionagainst radiation produced by magnetic-resonance imaging procedures.Moreover, it is desirable to provide devices that prevent the possibledamage that can be done at the tissue interface due to inducedelectrical signals and due to thermal tissue damage. Furthermore, it isdesirable to provide devices that do not interact with RF fields whichare emitted during magnetic-resonance imaging procedures and whichresult in degradation of the quality of the images obtained during theMRI process.

[0164] In one embodiment, there is provided a coating of nanomagneticparticles that consists of a mixture of aluminum oxide, iron, and otherparticles that have the ability to deflect electromagnetic fields whileremaining electrically non-conductive. Preferably the particle size insuch a coating is approximately 10 nanometers. Preferably the particlepacking density is relatively low so as to minimize electricalconductivity. Such a coating when placed on a fully or partiallymetallic object (such as a guidewire, catheter, stent, and the like) iscapable of deflecting electromagnetic fields, thereby protectingsensitive internal components, while also preventing the formation ofeddy currents in the metallic object or coating. The absence of eddycurrents in a metallic medical device provides several advantages, towit: (1) reduction or elimination of heating, (2) reduction orelimination of electrical voltages which can damage the device and/orinappropriately stimulate internal tissues and organs, and (3) reductionor elimination of disruption and distortion of a magnetic-resonanceimage.

[0165]FIGS. 13A, 13B, and 13C are schematic views of a catheter assemblysimilar to the assembly depicted in FIG. 2 of U.S. Pat. No. 3,995,623;the entire disclosure of such patent is hereby incorporated by referenceinto this specification. Referring to FIG. 6 of such patent, and also toFIGS. 13A, 13B, and 13C, it will be seen that catheter tube 625 containsmultiple lumens 603, 611, 613, and 615, which can be used for variousfunctions such as inflating balloons, enabling electrical conductors tocommunicate with the distal end of the catheter, etc. While four suchlumens are shown, it is to be understood that this invention applies toa catheter with any number of lumens.

[0166] The similar catheter disclosed and claimed in U.S. Pat. No.3,995,623 may be shielded by coating it in whole or in part with acoating of nanomagnetic particulate.

[0167] In the embodiment depicted in FIG. 13A, interior nanomagneticmaterial 650 a is applied to the interior wall of catheter 625, orexterior nanomagnetic material 650 b is applied to the exterior wall ofcatheter 625, or imbibed nanomagnetic material 650 c my be imbibed intothe walls of catheter 625, or any combination of these locations.

[0168] In the embodiment depicted in FIG. 13B, internal nanomagneticmaterial 650 d is applied to the interior walls of multiple lumens603/611/613/615 within a single catheter 625. Additionally, nonomagneticmaterials 650 b and 650 c are located on the external wall of catheter625 or imbibed into the common wall.

[0169] In the embodiment depicted in FIG. 13C, a nanomagnetic material650 e is applied to the mesh-like material 636 used within the wall ofcatheter 625 to give it desired mechanical properties.

[0170] In another embodiment (not shown) a sheath coated withnanomagnetic material on its internal surface, exterior surface, orimbibed into the wall of such sheath, is placed over a catheter toshield it from electromagnetic interference. In this manner, existingcatheters can be made MRI safe and compatible. The modified catheterassembly thus produced is resistant to electromagnetic radiation.

[0171]FIGS. 14A through 14G are schematic views of a catheter assembly700 consisting of multiple concentric elements. While two elements areshown; 720 and 722, it is to be understood that any number ofoverlapping elements may be used, either concentrically or planarlypositioned with respect to each other.

[0172] Referring to FIGS. 14A through 14G, and in the preferredembodiment depicted therein, it will be seen that catheter assembly 700comprises an elongated tubular construction having a single, central oraxial lumen 710. The exterior catheter body 722 and concentricallypositioned internal catheter body 720 with internal lumen 712 arepreferably flexible, i.e., bendable, but substantially non-compressiblealong its length. The catheter bodies 720 and 722 may be made of anysuitable material. A presently preferred construction comprises an outerwall 722 and inner wall 720 made of a polyurethane, silicone, or nylon.The outer wall 722 preferably comprises an imbedded braided mesh ofstainless steel or the like to increase torsional stiffness of thecatheter assembly 700 so that, when a control handle, not shown, isrotated, the tip sectionally of the catheter will rotate incorresponding manner. The catheter assembly 700 may be shielded bycoating it in whole or in part with a coating of nanomagneticparticulate, in any one or more of the following manners:

[0173] Referring to FIG. 14A, a nanomagnetic material 650 f may becoated on the outside surface of the inner concentrically positionedcatheter body 720.

[0174] Referring to FIG. 14B, a nanomagnetic material 650 g may becoated on the inside surface 713 of the inner concentrically positionedcatheter body 720.

[0175] Referring to FIG. 14C, a nanomagnetic material 650 h may beimbibed into the walls of the inner concentrically positioned catheterbody 720 and externally positioned catheter body 722. Although notshown, a nanomagnetic material may be imbibed solely into either innerconcentrically positioned catheter body 720 or externally positionedcatheter body 722.

[0176] Referring to FIG. 14D, a nanomagnetic material 650 f may becoated onto the exterior wall of the inner concentrically positionedcatheter body 720 and external wall 715 (see element 650 i). Referringto FIG. 14E, a nanomagnetic material 650 g may be coated onto theinterior wall 713 of the inner concentrically positioned catheter body720 and the external wall 715 of externally positioned catheter body722.

[0177] Referring to FIG. 14F, a nanomagnetic material 650 i may becoated on the outside surface 715 of the externally positioned catheterbody 722.

[0178] Referring to FIG. 14G, a nanomagnetic material 650 j may becoated onto the exterior surface of an internally positioned solidelement 727.

[0179] By way of further illustration, one may apply nanomagneticparticulate material to one or more of the catheter assemblies disclosedand claimed in U.S. Pat. Nos. 5,178,803; 5,041,083; 6,283,959;6,270,477; 6,258,080; 6,248,092; 6,238,408; 6,208,881; 6,190,379;6,171,295; 6,117,064; 6,019,736; 6,017,338; 5,964,757; 5,853,394; and6,235,024; the entire disclosure of which is hereby incorporated byreference into this specification. The catheters assemblies disclosedand claimed in the above-mentioned United States patents may be shieldedby coating them in whole or in part with a coating of nanomagmeticparticulate. The modified catheter assemblies thus produced areresistant to electromagnetic radiation.

[0180]FIGS. 15A, 15B, and 15C are schematic views of a guidewireassembly 800 for insertion into vascular vessel (not shown), and it issimilar to the assembly depicted in U.S. Pat. No. 5,460,187; the entiredisclosure of such patent is incorporated by reference into thisspecification. Referring to FIG. 15A, a coiled guidewire 810 is formedof a proximal section (not shown) and central support wire 820 whichterminates in hemispherical shaped tip 815. The proximal end has aretaining device (not shown) enables the person operating the guidewireto turn and orient the guidewire within the vascular conduit.

[0181] The guidewire assembly may be shielded by coating it in whole orin part with a coating of nanomagnetic particulate.

[0182] In the embodiment depicted in FIG. 15A; the nanomagnetic material650 is coated on the exterior surface of the coiled guidewire 810. Inthe embodiment depicted in FIG. 15B; the nanomagnetic material 650 iscoated on the exterior surface of the central support wire 820. In theembodiment depicted in FIG. 15C; the nanomagnetic material 650 is coatedon all guidewire assembly components including coiled guidewire 810, tip815, and central support wire 820. The modified guidewire assembly thusproduced is resistant to electromagnetic radiation.

[0183] By way of further illustration, one may coat with nanomagneticparticulate matter the guidewire assemblies disclosed and claimed inU.S. Pat. Nos.: 5,211,183; 6,168,604; 6,093,157; 6,019,737; 6,001,068;5,938,623; 5,797,857; 5,588,443; and 5,452,726; the entire disclosure ofwhich is hereby incorporated by reference into this specification. Themodified guidewire assemblies thus produced are resistant toelectromagnetic radiation.

[0184]FIGS. 16A and 16B are schematic views of a medical stent assembly900 similar to the assembly depicted in FIG. 15 of U.S. Pat. No.5,443,496; the entire disclosure of such patent is hereby incorporatedby reference into this specification.

[0185] Referring to FIG. 16A, a self-expanding stent 900 comprisingjoined metal stent elements 962 is shown. The stent 960 also comprises aflexible film 964. The flexible film 964 can be applied as a sheath tothe metal stent elements 962 after which the stent 900 can becompressed, attached to a catheter, and delivered through a body lumento a desired location. Once in the desired location, the stent 900 canbe released from the catheter and expanded into contact with the bodylumen, where it can conform to the curvature of the body lumen. Theflexible film 964 is able to form folds, which allow the stent elementsto readily adapt to the curvature of the body lumen. The medical stentassembly disclosed and claimed in U.S. Pat. No. 5,443,496 may beshielded by coating it in whole or in part with a nanomagnetic coating.

[0186] In the embodiment depicted in FIG. 16A, flexible film 964 iscoated with a nanomagnetic coating on its inside or outside surfaces, orwithin the film itself.

[0187] In one embodiment, a stent (not shown) is coated with ananomagnetic material.

[0188] It is to be understood that any one of the above embodiments maybe used independently or in conjunction with one another within a singledevice.

[0189] In yet another embodiment (not shown), a sheath (not shown),coated or imbibed with a nanomagnetic material is placed over the stent,particularly the flexible film 964, to shield it from electromagneticinterference. In this manner, existing stents can be made MRI safe andcompatible.

[0190] By way of further illustration, one may coat one or more of themedical stent assemblies disclosed and claimed in U.S. Pat. Nos.:6,315,794; 6,190,404; 5,968,091; 4,969,458; 6,342,068; 6,312,460;6,309,412; and 6,305,436; the entire disclosure of each of which ishereby incorporated by reference into this specification. The medicalstent assemblies disclosed and claimed in the above-mentioned UnitedStates patents may be shielded by coating them in whole or in part witha coating of nanomagmetic particulate, as described above. The modifiedmedical stent assemblies thus produced are resistant to electromagneticradiation.

[0191]FIG. 17 is a schematic view of a biopsy probe assembly 1000similar to the assembly depicted in FIG. 1 of U.S. Pat. No. 5,005,585;the entire disclosure of such patent is hereby incorporated by referenceinto this specification. Such biopsy probe assembly 1000 is composed ofthree separate components, a hollow tubular cannula or needle 1001, asolid intraluminar rod-like stylus 1002, and a clearing rod or probe(not shown).

[0192] The components of the assembly 1000 are preferably formed of analloy, such as stainless steel, which is corrosion resistant andnon-toxic. Cannula 1001 has a proximal end (not shown) and a distal end1005 that is cut at an acute angle with respect to the longitudinal axisof the cannula and provides an annular cutting edge.

[0193] By way of further illustration, biopsy probe assemblies aredisclosed and claimed in U.S. Pat. Nos.: 4,671,292; 5,437,283;5,494,039; 5,398,690; and 5,335,663; the entire disclosure of each ofwhich is hereby incorporated by reference into this specification. Thebiopsy probe assemblies disclosed and claimed in the above-mentionedUnited States patents may be shielded by coating them in whole or inpart with a coating of nanomagmetic particulate. Thus, e.g., cannula1001 may be coated, intraluminar stylus 1002 may be coated, and/or theclearing rod may be coated.

[0194] In one variation on this design (not shown), a biocompatiblesheath is placed over the coated cannula 1001 to protect thenanomagnetic coating from abrasion and from contacting body fluids.

[0195] In another embodiment, the biocompatible sheath has on itsinterior surface or within its walls a nanomagnetic coating.

[0196] In yet another embodiment (not shown), a sheath coated or imbibedwith a nanomagnetic material is placed over the biopsy probe, to shieldit from electromagnetic interference. The modified biopsy probeassemblies thus produced are resistant to electromagnetic radiation.

[0197]FIGS. 18A and 18B are schematic views of a flexible tube endoscopesheath assembly 1100 similar to the assembly depicted in FIG. 1 of U.S.Pat. No. 5,058,567; the entire disclosure of such patent is herebyincorporated by reference into this specification.

[0198] MRI is increasingly being used interoperatively to guide theplacement of medical devices such as endoscopes which are very good attreating or examining tissues close up, but generally cannot accuratelydetermine where the tissues being examined are located within the body.

[0199] Referring to FIG. 18A, the endoscope 1100 employs a flexible tube1110 with a distally positioned objective lens 1120. Flexible tube 1110is preferably formed in such manner that the outer side of a spiral tubeis closely covered with a braided-wire tube (not shown) formed byweaving fine metal wires into a braid. The spiral tube is formed using aprecipitation hardening alloy material, for example, beryllium bronze(copper-beryllium alloy).

[0200] By way of further illustration, other endoscope tube assembliesare disclosed and claimed in U.S. Pat. Nos.: 4,868,015; 4,646,723;3,739,770; 4,327,711; and 3,946,727; the entire disclosure of each ofwhich is hereby incorporated by reference into this specification. Theendoscope tube assemblies disclosed and claimed in the above-mentionedUnited States patents may be shielded by coating them in whole or inpart with a coating of nanomagmetic particulate, material as describedelsewhere in this specification.

[0201] Referring again to FIG. 18A; sheath 1180 is a sheath coated withnanomagnetic material 650 a/650 b/650 c on its inside surface, itsexterior surface, or imbibed into its structure; and such sheath 1180 isplaced over the endoscope 1100, particularly the flexible tube 1110, toshield it from electromagnetic interference.

[0202] In yet another embodiment (not shown), flexible tube 1110 iscoated with nanomagnetic materials on its internal surface, or imbibedwith nanomagnetic materials within its wall.

[0203] In another embodiment (not shown), the braided-wire elementwithin flexible tube 1110 is coated with a nanomagnetic material.

[0204] In this manner, existing endoscopes can be made MRI safe andcompatible. The modified endoscope tube assemblies thus produced areresistant to electromagnetic radiation.

[0205]FIGS. 19A and 19B are schematic illustrations of a sheath assembly2000 comprised of a sheath 2002 whose surface 2004 is comprised of amultiplicity of nanomagnetic materials 2006, 2008, and 2010. In oneembodiment, the nanomagnetic material consists of or comprisesnanomagnetic liquid crystal material. Additionally, nanomagneticmaterials 2006, 2008, and 2010 may be placed on the inside surface ofsheath 2002, imbibed into the wall of sheath 2002, or any combination ofthese locations.

[0206] The sheath 2002 may be formed from electrically conductivematerials that include metals, carbon composites, carbon nanotubes,metal-coated carbon filaments (wherein the metal may be either aferromagnetic material such as nickel, cobalt, or magnetic ornon-magnetic stainless steel; a paramagnetic material such as titanium,aluminum, magnesium, copper, silver, gold, tin, or zinc; a diamagneticmaterial such as bismuth, or well known superconductor materials),metal-coated ceramic filaments (wherein the metal may be one of thefollowing metals: nickel, cobalt, magnetic or non-magnetic stainlesssteel, titanium, aluminum, magnesium, copper, silver, gold, tin, zinc,bismuth, or well known superconductor materials, a composite ofmetal-coated carbon filaments and a polymer (wherein the polymer may beone of the following: polyether sulfone, silicone, polyimide, polyamide,polyvinylidene fluoride, epoxy, or urethane), a composite ofmetal-coated ceramic filaments and a polymer (wherein the polymer may beone of the following: polyether sulfone, silicone, polyimide, polyamide,polyvinylidene fluoride, epoxy, or urethane), a composite ofmetal-coated carbon filaments and a ceramic (wherein the ceramic may beone of the following: cement, silicates, phosphates, silicon carbide,silicon nitride, aluminum nitride, or titanium diboride), a composite ofmetal-coated ceramic filaments and a ceramic (wherein the ceramic may beone of the following: cement, silicates, phosphates, silicon carbide,silicon nitride, aluminum nitride, or titanium diboride), or a compositeof metal-coated (carbon or ceramic) filaments (wherein the metal may beone of the following metals: nickel, cobalt, magnetic or non-magneticstainless steel, titanium, aluminum, magnesium, copper, silver, gold,tin, zinc, bismuth, or well known superconductor materials), and apolymer/ceramic combination (wherein the polymer may be one of thefollowing: polyether sulfone, silicone, polymide, polyvinylidenefluoride, or epoxy and the ceramic may be one of the following: cement,silicates, phosphates, silicon carbide, silicon nitride, aluminumnitride, or titanium diboride).

[0207] In one preferred embodiment, the sheath 2002 is comprised of atleast about 50 volume percent of the nanomagnetic material describedelsewhere in this specification.

[0208] As is known to those skilled in the art, liquid crystals arenonisotropic materials (that are neither crystalline nor liquid)composed of long molecules that, when aligned, are parallel to eachother in long clusters. These materials have properties intermediatethose of crystalline solids and liquids. See, e.g., page 479 of GeorgeS. Brady et al.'s “Materials Handbook,” Thirteenth Edition (McGraw-Hill,Inc., New York, 1991).

[0209] Ferromagnetic liquid crystals are known to those in the art, andthey are often referred to as FMLC. Reference may be had, e.g., to U.S.Pat. Nos. 4,241,521; 6,451,207; 5,161,030; 6,375,330; 6,130,220; and thelike. The entire disclosure of each of these United States patents ishereby incorporated by reference into this specification.

[0210] Reference also may be had to U.S. Pat. No. 5,825,448, whichdescribes a reflective liquid crystalline diffractive light valve. Thefigures of this patent illustrate how the orientations of the magneticliquid crystal particles align in response to an applied magnetic field.The entire disclosure of this United States patent is herebyincorporated by reference into this specification.

[0211] Referring again to FIG. 19A, and in the embodiment depictedtherein, it will be seen that sheath 2002 may be disposed in whole or inpart over medical device 2012. In the embodiment depicted, the sheath2002 is shown as being bigger than the medical device 2012. It will beapparent that such sheath 2002 may be smaller than the medical device2012, may be the same size as the medical device 2012, may have adifferent cross-sectional shape than the medical 2012, and the like.

[0212] In one preferred embodiment, the sheath 2002 is disposed over themedical device 2012 and caused to adhere closely thereto. One may createthis adhesion either by use of adhesive(s) and/or by mechanicalshrinkage.

[0213] In one embodiment, shrinkage of the sheath 2012 is caused byheat, utilizing well known shrink tube technology. Reference may be had,e.g., to U.S. Pat. Nos. 6,438,229; 6,245,053; 6,082,760; 6,055,714;5,903,693; and the like. The entire disclosure of each of these UnitedStates patents is hereby incorporated by reference into thisspecification.

[0214] In another embodiment of the invention, the sheath 2002 is arigid or flexible tube formed from polytetrafluoroethylene that is heatshrunk into resilient engagement with the implantable medical device.The sheath can also be formed from heat shrinkable polymer materialse.g., low density polyethylene (LDPE), linear low-density polyethylene(LLDPE), ethylene vinyl acrylate (EVA), ethylene methacrylate (EMA),ethylene methacrylate acid (EMAA) and ethyl glycol methacrylic acid(EGMA). The polymer material of the heat shrinkable sheath should have aVicat softening point less than 50 degrees Centigrade and a melt indexless than 25. A particularly suitable polymer material for the sheath ofthe invention is a copolymer of ethylene and methyl acrylate which isavailable under the trademark Lotryl 24MA005 from Elf Atochem. Thiscopolymer contains 25% methyl acrylate, has a Vicat softening point ofabout 43 degree centigrade and a melt index of about 0.5.

[0215] In another embodiment of the invention, the sheath 2002 is acollapsible tube that can be extended over the implantable medicaldevice such as by unrolling or stretching.

[0216] In yet another embodiment of the invention, the sheath 2002contains a tearable seam along its axial length, to enable the sheath tobe withdrawn and removed from the implantable device without explantingthe device or disconnecting the device from any attachments to itsproximal end, thereby enabling the electromagnetic shield to be removedafter the device is implanted in a patient. This is a preferable featureof the sheath, since it eliminates the need to disconnect any devicesconnected to the proximal (external) end of the device, which couldinterrupt the function of the implanted medical device. This feature isparticularly critical if the shield is being applied to alife-sustaining device, such as a temporary implantable cardiacpacemaker.

[0217] The ability of the sheath 1180 (see FIGS. 18A/18B) or 2002 (seeFIGS. 19A/19B) to be easily removed, and therefore easily disposed,without disposing of the typically much more expensive medical devicebeing shielded, is a preferred feature since it preventscross-contamination between patients using the same medical device.

[0218] In still another embodiment of the invention, an activelycirculating, heat-dissipating fluid can be pumped into one or moreinternal channels within the sheath. The heat-dissipation fluid willdraw heat to another region of the device, including regions locatedoutside of the body where the heat can be dissipated at a faster rate.The heat-dissipating flow may flow internally to the layer ofnanomagnetic particles, or external to the layer of nanomagneticparticulate material.

[0219]FIG. 19B illustrates a process 2001 in which heat 2030 is appliedto a shrink tube assembly 2003 to produce the final product 2005. Forthe sake of simplicity of representation, the controller 2007 has beenomitted from FIG. 19B.

[0220] Referring again to FIG. 19A, and in the preferred embodimentdepicted therein, it will be seen that a controller 2007 is connected byswitch 2009 to the sheath 2002. A multiplicity of sensors 2014 and 2016,e.g., can detect the effectiveness of sheath 2002 by measuring, e.g.,the temperature and/or the electromagnetic field strength within theshield 2002. One or more other sensors 2018 are adapted to measure theproperties of sheath 2002 at its exterior surface 2004.

[0221] For the particular sheath embodiment utilizing a liquid crystalnanomagnetic particle construction, and depending upon the data receivedby controller 2007, the controller 2007 may change the shieldingproperties of shield 2002 by delivering electrical and/or magneticenergy to locations 2030, 2022, 2024, etc. The choice of the energy tobe delivered, and its intensity, and its location, and its duration,will vary depending upon the status of the sheath 2002.

[0222] In the embodiment depicted in FIG. 19, the medical device may bemoved in the direction of arrow 2026, while the sheath 2002 may be movedin the direction of arrow 2028, to produce the assembly 2001 depicted inFIG. 19B. Thereafter, heat may be applied to this assembly to producethe assembly 2005 depicted in FIG. 19B.

[0223] In one embodiment, not shown, the sheath 2002 is comprised of anelongated element consisting of a proximal end and a distal end,containing one or more internal hollow lumens, whereby the lumens atsaid distal end may be open or closed, is used to temporarily orpermanently encase an implantable medical device.

[0224] In this embodiment, the elongated hollow element is similar tothe sheath disclosed and claimed in U.S. Pat. No. 5,964,730; the entiredisclosure of which is hereby incorporated by reference into thisspecification.

[0225] Referring again to FIG. 19A, and in the embodiment depictedtherein, the sheath 2002 is preferably coated and/or impregnated withnanomagnetic shielding material 2006/2008/2010 that comprises at least50 percent of its external surface, and/or comprises at least 50 percentof one or more lumen internal surfaces, or imbibed within the wall 2015of sheath 2002, thereby protecting at least fifty percent of the surfacearea of one or more of its lumens, or any combination of these surfacesor areas, thus forming a shield against electromagnetic interference forthe encased medical device.

[0226]FIG. 20A is a schematic of a multiplicity of liquid crystals 2034,2036, 2038, 2040, and 2042 disposed within a matrix 2032. As will beapparent, each of these liquid crystals is comprised of nanomagneticmaterial 2006. In the configuration illustrated in FIG. 20A, the liquidcrystals 2034 et seq. are not aligned.

[0227] By comparison, in the configuration depicted in FIG. 20B, suchliquid crystals 2034 are aligned. Such alignment is caused by theapplication of an external energy field (not shown).

[0228] The liquid crystals disposed within the matrix 2032 (see FIGS.20A through 20F) may have different concentrations and/or compositionsof nanomagnetic particles 2006, 2009, and/or 2010; see FIG. 20C andliquid crystals 2044, 2046, 2048, 2050, and 2052. Alternatively, oradditionally, the liquid crystals may have different shapes; see FIGS.20D, 20E, and 20F and liquid crystals 2054 and 2056, 2058, 2060, 2062,2064, and 2066. As will be apparent, by varying the size, shape, number,location, and/or composition of such liquid crystals, one may customdesign any desired response.

[0229]FIG. 21 is a graph of the response of a typical matrix 2032comprised of nanomagnetic liquid crystals. Three different curves,curves 2068, 2070, and 2072, are depicted, and they correspond to theresponses of three different nanomagnetic liquid crystal materials havedifferent shapes and/or sizes and/or compositions.

[0230] Referring to FIG. 21, and for each of curves 2068 through 2072,it will be seen that there is often a threshold point 2074 below whichno meaningful response to the applied magnetic field is seen; see, e.g.,the response for curve 2070.

[0231] It should be noted, however, that some materials have a lowthreshold before they start to exhibit response to the applied magneticfield; see, e.g., curve 2068. On the other hand, some materials have avery large threshold; see, e.g., threshold 2076 for curve 2072.

[0232] One may produce any desired response curve by the propercombination of nanomagnetic material composition, concentration, andlocation as well as liquid crystal geometries, materials, and sizes.Other such variables will be apparent to those skilled in the art.

[0233] Referring again to FIG. 21, it will be seen that there often is amonotonic region 2078 in which the increase of alignment of thenanomagnetic material is monotonic and often directly proportional; see,e.g., curve 2070.

[0234] There also is often a saturation point 2080 beyond which anincrease in the applied magnetic field does not substantially increasethe alignment.

[0235] As will be seen from the curves in FIG. 21, the process often isreversible. One may go from a higher level of alignment to a lower levelby reducing the magnetic field applied.

[0236] The frequency of the magnetic field applied also influences thedegree of alignment. As is illustrated in FIG. 22, for one nanomagneticliquid crystal material (curve 2082), the response is at a maximum at aninitial frequency 2086 but then decreases to a minimum at frequency2088. By comparison, for another such curve (curve 2084), the responseis minimum at frequency 2086, increases to a maximum at point 2090, andthen decreases to a minimum at point 2092.

[0237] Thus, one may influence the response of a particular nanomagneticliquid crystal material by varying its type of nanomagnetic material,and/or its concentration, and/or its shape, and/or the frequency towhich it is subjected. Referring again to FIG. 19A, one may affect theshielding effectiveness of shield 2002 by supplying a secondary magneticfield (from controller 2007) at the secondary frequencies which willelicit the desired shielding effect.

[0238]FIG. 23 is a flow diagram illustrating a preferred process 2094for making nanomagnetic liquid crystal material.

[0239] Referring to FIG. 23, and in step 2100, the nanomagnetic materialof this invention is charged to a mixer 2102 via line 2104. Thereafter,suspending medium is also charged to the mixer 2102 via line 2106.

[0240] The suspending medium may be any medium in which the nanomagneticmaterial is dispersible. Thus, e.g., the suspending medium may be a gel,it may be an aqueous solution, it may be an organic solvent, and thelike. In one embodiment, the nanomagnetic material is not soluble in thesuspending medium; in this embodiment, a slurry is produced. For thesake of simplicity of description, the use of a polymer will bedescribed in the rest of the process.

[0241] Referring again to FIG. 23, the slurry from mixer 2102 is chargedvia line 2108 to mixer 2110. Thereafter, or simultaneously, polymericprecursor of liquid crystal material is also charged to mixer 2102 vialine 2104.

[0242] As is known to those skilled in the art, aromatic polyesters(liquid crystals) may be used as such polymeric precursor. Thesearomatic polyesters are commercially available as, e.g., Vectra (sold byHoechst Celanese Engineering Plastic), Xydur (sold by Amoco PerformancePlastics), Granlar (sold by Granmont), and the like. Reference may behad, e.g., to pages 649-650 of the aforementioned “Materials Handbook.”Reference also may be had, e.g., to U.S. Pat. Nos. 4,738,880; 5,142,017;5,006,402; 4,935,833; and the like. The entire disclosure of each ofthese United States patents is hereby incorporated by reference intothis specification.

[0243] Referring again to FIG. 23, the liquid crystal polymer is mixedwith the nanomagnetic particles for a time sufficient to produce asubstantially homogeneous mixture. Typically, mixing occurs from about 5to about 60 minutes.

[0244] The polymeric material formed in mixer 2110 then is formed into adesired shape in former 2113. Thus, and referring to Joel Frados'“Plastics Engineering Handbook,” Fourth Edition (Van Nostrand ReinholdCompany, New York, N.Y., 1976), one may form the desired shape byinjection molding, extrusion, compression and transfer molding, coldmolding, blow molding, rotational molding, casting, machining, joining,and the like. Other such forming procedures are well known to thoseskilled in the art.

[0245] One may prepare several different nanomagnetic structures andjoin them together to form a composite structure. One such compositestructure is illustrated in FIG. 24.

[0246] Referring to FIG. 24, assembly 2120 is comprised of nanomagneticparticles 2006, 2010, and 2008 disposed in layers 2122, 2124, and 2126,respectively. In the embodiment depicted, the layers 2122, 2124, and2126 are contiguous with each, thereby forming a continuous assembly ofnanomagnetic material, with different concentrations and compositionsthereof at different points. The response of assembly 2120 to anyparticular magnetic field will vary depending upon the location at whichsuch response is measured.

[0247]FIG. 25 illustrates an assembly 2130 that is similar to assembly2120 but that contains an insulating layer 2132 disposed betweennanomagnetic layers 2134 and 2136. The insulating layer 2132 may beeither electrically insulative and/or thermally insulative.

[0248]FIG. 26 illustrates an assembly 2140 in which the response ofnanomagnetic material 2142 to an applied field 2143 is sensed by sensor2144 that, in the embodiment depicted, is a pickup coil 2144. Data fromsensor 2144 is transmitted to controller 2146. When and as appropriate,controller 2146 may introduce electrical and/or magnetic energy intoshielding material 2142 in order to modify its response.

[0249]FIG. 27 is a schematic illustration of an assembly 2150. In theembodiment depicted, concentric insulating layers 2152 and 2154preferably have substantially different thermal conductivities. Layer2152 preferably has a thermal conductivity that is in the range of fromabout 10 to about 2000 calories per hour per square centimeter percentimeter per degree Celsius. Layer 2154 has a thermal conductivitythat is in the range of from about 0.2 to about 10 calories per hour persquare centimeter per centimeter per degree Celsius. Layers 2152 and2154 are designed by choice of thermal conductivity and of layerthickness such that heat is conducted axially along, andcircumferentially around, layer 2152 at a rate that is between 10 timesand 1000 times higher than in layer 2154. Thus, in this embodiment, anyheat that is generated at any particular site or sites in one or morenanomagnetic shielding layers will be distributed axially along theshielded element, and circumferentially around it, before beingconducted radially to adjoining tissues. This will serve to furtherprotect these adjoining tissues from thermogenic damage even if thereare minor local flaws in the nanomagnetic shield.

[0250] Thus, in one embodiment of the invention, there is described amagnetically shielded conductor assembly, that contains a conductor, atleast one layer of nanomagnetic material, a first thermally insulatinglayer, and a second thermally insulating layer. The first thermalinsulating layer resides radially inward from said second thermallyinsulating layer, and it has a thermal conductivity from about 10 toabout 2000 calories-centimeter per hour per square centimeter per degreeCelsius. The second thermal insulating layer has a thermal conductivityfrom about 0.2 to about 10 calories per hour per square centimeter perdegree Celsius, and the axial and circumferential heat conductance ofthe first thermal insulating layer is at least about 10 to about 1000times higher than it is for said second thermal insulating layer.

[0251] In another embodiment of the invention, there is provided amagnetically shielded conductor assembly as discussed hereinabove, inwhich the first thermally insulating layer is disposed between saidconductor and said layer of nanomagnetic material, and the secondthermally insulating layer is disposed outside said layer ofnanomagnetic material

[0252] In another embodiment, there is provided a magnetically shieldedconductor assembly as discussed hereinabove wherein the first thermallyinsulating layer is disposed outside the layer of nanomagnetic material,and wherein the second thermally insulating layer is disposed outsidesaid first layer of thermally insulating material.

[0253] In another embodiment, the shield is comprised of aabrasion-resistant coating comprised of nanomagnetic material. Referringto FIG. 28, it will be seen that shield 2170 is comprised of abrasionresistant coating 2172 and nanomagnetic layer 2174.

[0254] A Composite Shield

[0255] In this portion of the specification, applicants will describeone embodiment of a composite shield of their invention. This embodimentinvolves a shielded assembly comprised of a substrate and, disposedabove a substrate, a shield comprising from about 1 to about 99 weightpercent of a first nanomagnetic material, and from about 99 to about 1weight percent of a second material with a resistivity of from about 1microohm-centimeter to about 1×10²⁵ microohm centimeters.

[0256]FIG. 29 is a schematic of a preferred shielded assembly 3000 thatis comprised of a substrate 3002. The substrate 3002 may be any one ofthe substrates illustrated hereinabove. Alternatively, or additionally,it may be any receiving surface which it is desired to shield frommagnetic and/or electrical fields. Thus, e.g., the substrate can besubstantially any size, any shape, any material, or any combination ofmaterials. The shielding material(s) disposed on and/or in suchsubstrate may be disposed on and/or in some or all of such substrate.

[0257] By way of illustration and not limitation, the substrate 3002 maybe, e.g., a foil comprised of metallic material and/or polymericmaterial. The substrate 3002 may, e.g., comprise ceramic material, glassmaterial, composites, etc. The substrate 3002 may be in the shape of acylinder, a sphere, a wire, a rectilinear shaped device (such as a box),an irregularly shaped device, etc.

[0258] In one embodiment, the substrate 3002 preferably has a thicknessof from about 100 nanometers to about 2 centimeters. In one aspect ofthis embodiment, the substrate 3002 preferably is flexible.

[0259] Referring again to FIG. 29, and in the preferred embodimentdepicted therein, it will be seen that a shield 3004 is disposed abovethe substrate 3002. As used herein, the term “above” refers to a shieldthat is disposed between a source 3006 of electromagnetic radiation 102and the substrate 3002. The shield 3004 may be contiguous with thesubstrate 3002, or it may not be contiguous with the substrate 3002.

[0260] The shield 3004, in the embodiment depicted, is comprised of fromabout 1 to about 99 weight percent of nanomagnetic material 3008; suchnanomagnetic material, and its properties, are described elsewhere inthis specification. In one embodiment, the shield 3004 is comprised ofat least about 40 weight percent of such nanomagnetic material 3008. Inanother embodiment, the shield 3004 is comprised of at least about 50weight percent of such nanomagnetic material 3008.

[0261] Referring again to FIG. 29, and in the preferred embodimentdepicted therein, it will be seen that the shield 3004 is also comprisedof another material 3010 that preferably has an electrical resistivityof from about about 1 microohm-centimeter to about 1×10²⁵microohm-centimeters. This material 3010 is preferably present in theshield at a concentration of from about 1 to about 99 weight percentand, more preferably, from about 40 to about 60 weight percent.

[0262] In one embodiment, the material 3010 has a dielectric constant offrom about 1 to about 50 and, more preferably, from about 1.1 to about10. In another embodiment, the material 3010 has resistivity of fromabout 3 to about 20 microohm-centimeters.

[0263] In one embodiment, the material 3010 preferably is ananoelectrical material with a particle size of from about 5 nanometersto about 100 nanometers.

[0264] In another embodiment, the material 3010 has an elongated shapewith an aspect ratio (its length divided by its width) of at least about10. In one aspect of this embodiment, the material 3010 is comprised ofa multiplicity of aligned filaments.

[0265] In one embodiment, the material 3010 is comprised of one or moreof the compositions of U.S. Pat. No. 5,827,997 and 5,643,670. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification.

[0266] Thus, e.g., the material 3010 may comprise filaments, whereineach filament comprises a metal and an essentially coaxial core, eachfilament having a diameter less than about 6 microns, each corecomprising essentially carbon, such that the incorporation of 7 percentvolume of this material in a matrix that is incapable of electromagneticinterference shielding results in a composite that is substantiallyequal to copper in electromagnetic interference shielding effectives at1-2 gigahertz. Reference may be had, e.g., to U.S. Pat. No. 5,827,997.

[0267] In another embodiment, the material 3010 is a particulate carboncomplex comprising: a carbon black substrate, and a plurality of carbonfilaments each having a first end attached to said carbon blacksubstrate and a second end distal from said carbon black substrate,wherein said particulate carbon complex transfers electrical current ata density of 7000 to 8000 milliamperes per square centimeter for aFe⁺²/Fe⁺³ oxidation/reduction electrochemical reaction couple carriedout in an aqueous electrolyte solution containing 6 millmoles ofpotassium ferrocyanide and one mole of aqueous potassium nitrate.

[0268] In another embodiment, the material 3010 is a diamond-like carbonmaterial. As is known to those skilled in the art, this diamond-likecarbon material has a Mohs hardness of from about 2 to about 15 and,preferably, from about 5 to about 15. Reference may be had, e.g., toU.S. Pat. No. 5,098,737 (amorphic diamond material); U.S. Pat. No.5,658,470 (diamond-like carbon for ion milling magnetic material);5,731,045 (application of diamond-like carbon coatings to tungstencarbide components); U.S. Pat. No. 6,037,016 (capacitatively coupledradio frequency diamond-like carbon reactor); U.S. Pat. No. 6,087,025(application of diamond like material to cutting surfaces), and thelike. The entire disclosure of each of these United States patents ishereby incorporated by reference into this specification.

[0269] In another embodiment, material 3010 is a carbon nanotubematerial. These carbon nanotubes generally have a cylindrical shape witha diameter of from about 2 nanometers to about 100 nanometers, andlength of from about 1 micron to about 100 nicrons.

[0270] These carbon nanotubes are well known to those skilled in theart. Reference may be had, e.g., to U.S. Pat. No. 6,203,864(heterojunction comprised of a carbon nanotube), U.S. Pat. No. 6,361,861(carbon nanotubes on a substrate), U.S. Pat. No. 6,445,006(microelectronic device comprising carbon nanotube components), U.S.Pat. No. 6,457,350 (carbon nanotube probe tip), and the like. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification.

[0271] In one embodiment, material 3010 is silicon dioxide particulatematter with a particle size of from about 10 nanometers to about 100nanometers.

[0272] In another embodiment, the material 3010 is particulate alumina,with a particle size of from about 10 to about 100 nanometers.Alternatively, or additionally, one may use aluminum nitride particles,cerium oxide particles, yttrium oxide particles, combinations thereof,and the like; regardless of the particle(s) used in this embodiment, itis preferred that its particle size be from about 10 to about 100nanometers.

[0273] In the embodiment depicted in FIG. 29, the shield 3004 ispreferably in the form of a layer of material that has a thickness offrom about 100 nanometers to about 10 microns. In this embodiment, boththe nanomagnetic particles 3008 and the electrical particles 3010 arepresent in the same layer.

[0274] In the embodiment depicted in FIG. 30, by comparison, the shield3012 is comprised of layers 3014 and 3016. The layer 3014 is comprisedof at least about 50 weight percent of nanomagnetic material 3008 and,preferably, at least about 90 weight percent of such nanomagneticmaterial 3008. The layer 3016 is comprised of at least about 50 weightpercent of electrical material 3010 and, preferably, at least about 90weight percent of such electrical material 3010.

[0275] In the embodiment depicted in FIG. 30, the layer 3014 is disposedbetween the substrate 3002 and the layer 3016. In the embodimentdepicted in FIG. 31, the layer 3016 is disposed between the substrate3002 and the layer 3014.

[0276] Each of the layers 3014 and 3016 preferably has a thickness offrom about 10 nanometers to about 5 microns.

[0277] In one embodiment, the shield 3012 has an electromagneticshielding factor of at least about 0.5 and, more preferably, at leastabout 0.9. In one embodiment, the electromagnetic field strength atpoint 3020 is no greater than about 10 percent of the electromagneticfield strength at point 3022.

[0278] In one preferred embodiment, illustrated in FIG. 31, thenanomagnetic material 3008 and/or 3010 preferably has a mass density ofat least about 0.01 grams per cubic centimeter, a saturationmagnetization of from about 1 to about 36,000 Gauss, a coercive force offrom about 0.01 to about 5000 Oersteds, a relative magnetic permeabilityof from about 1 to about 500,000, and an average particle size of lessthan about 100 nanometers.

[0279] Determination of the Heat Shielding Effect of the Magnetic Shield

[0280]FIG. 32 is a schematic representation of a test which may be usedto determine the extent to which the temperature of a conductor 4000 israised by exposure to strong electromagnetic radiation 3006. In thistest, the radiation 3006 is representative of the fields present duringMRI procedures. As is known to those skilled in the art, such fieldstypically include a static field with a strength of from about 0.5 toabout 2 Teslas, a radio frequency alternating magnetic field with astrength of from about 20 microTeslas to about 100 nicroTeslas, and agradient magnetic field that has three components—x, y, and z, each ofwhich has a field strength of from about 0.05 to 500 milliteslas.

[0281] The test depicted in FIG. 32 is conducted in accordance withA.S.T.M. Standard Test F-2182-02, “Standard test method for measurementof radio-frequency induced heating near passive implant during magneticresonance imaging.” Referring again to FIG. 32, a temperature probe 4002is used to measure the temperature of an unshielded conductor 4000 whensubjected to the magnetic field 3006 in accordance with such A.S.T.M.F-2182-02.

[0282] The same test is then performed upon a shielded conductorassembly 4010 that is comprised of the conductor 4000 and a magneticshield 4004, as shown in FIG. 33.

[0283] The magnetic shield used may comprise nanomagnetic particles, asdescribed hereinabove. Alternatively, or additionally, it may compriseother shielding material, such as, e.g., oriented nanotubes (see, e.g.,U.S. Pat. No. 6,265,466). The entire disclosure of this United Statespatent is hereby incorporated by reference into this specification.

[0284] In the embodiment depicted in FIG. 33, the shield 4004 is in theform of a layer of shielding material with a thickness 4006 of fromabout 10 nanometers to about 1 millimeter. In one embodiment, thethickness 4006 is from about 10 nanometers to about 20 microns.

[0285] In one preferred embodiment, illustrated in FIG. 33, the shieldedconductor 4010 is implantable device and is connected to a pacemakerassembly 4012 comprised of a power source 4014, a pulse generator 4016,and a controller 4018. The pacemaker assembly 4012 and its associatedshielded conductor 4010 are preferably disposed within a livingbiological organism 4020.

[0286] Referring again to FIG. 33, and in the preferred embodimentdepicted therein, it will be seen that shielded conductor assembly 4010comprises a means 4011 for transmitting signals to and from thepacemaker 4012 and the biological organism 4020.

[0287] In one preferred embodiment, the conductor 4000 is flexible, thatis, at least a portion 4022 of the conductor 4000 is capable of beingflexed at an angle 4024 of least 15 degrees by the application of aforce 4026 not to exceed about 1 dyne.

[0288] Referring again to FIG. 33, when the shielded assembly is testedin accordance with A.S.T.M. 2182-02, it will have a specifiedtemperature increase, as is illustrated in FIG. 34.

[0289] As is shown in FIG. 34, the “dTs” is the change in temperature ofthe shielded assembly 4010 when tested in accordance with such A.S.T.M.test. The “dTc” is the change in temperature of the unshielded conductor4000 using precisely the same test conditions but omitting the shield4004. The ratio of dTs/dTc is the temperature increase ratio; and thetemperature increase ratio is defined as the heat shielding factor.

[0290] It is preferred that the shielded conductor assembly 4010 have aheat shielding factor of less than about 0.2. In one embodiment, theshielded conductor assembly 4010 has a heat shielding factor of lessthan about least 0.3.

[0291]FIGS. 35 and 36 are sectional views of shielded conductor assembly4030 and 4032. Each of these assemblies is comprised of a flexibleconductor 4000, a layer 4004 of magnetic shielding material, and asheath 4034.

[0292] The sheath 4034 preferably is comprised of antithrombogenicmaterial. In one embodiment, the sheath 4034 preferably has acoefficient of friction of less than about 0.1.

[0293] Antithrombogenic compositions and structures have been well knownto those skilled in the art for many years. As is disclosed, e.g., inU.S. Pat. No. 5,783,570, the entire disclosure of which is herebyincorporated by reference into this specification, “Artificial materialssuperior in processability, elasticity and flexibility have been widelyused as medical materials in recent years. It is expected that they willbe increasingly used in a wider area as artificial organs such asartificial kidney, artificial lung, extracorporeal circulation devicesand artificial blood vessels, as well as disposable products such assyringes, blood bags, cardiac catheters and the like. These medicalmaterials are required to have, in addition to sufficient mechanicalstrength and durability, biological safety which particularly means theabsence of blood coagulation upon contact with blood, i.e.,antithrombogenicity.”

[0294] “Conventionally employed methods for impartingantithrombogenicity to medical materials are generally classified intothree groups of (1) immobilizing a mucopolysaccharide (e.g., heparin) ora plasminogen activator (e.g., urokinase) on the surface of a material,(2) modifying the surface of a material so that it carries negativecharge or hydrophilicity, and (3) inactivating the surface of amaterial. Of these, the method of (1) (hereinafter to be referred tobriefly as surface heparin method) is further subdivided into themethods of (A) blending of a polymer and an organic solvent-solubleheparin, (B) coating of the material surface with an organicsolvent-soluble heparin, (C) ionic bonding of heparin to a cationicgroup in the material, and (D) covalent bonding of a material andheparin.”

[0295] “Of the above methods, the methods (2) and (3) are capable ofaffording a stable antithrombogenicity during a long-term contact withbody fluids, since protein adsorbs onto the surface of a material toform a biomembrane-like surface. At the initial stage when the materialhas been introduced into the body (blood contact site) and when variouscoagulation factors etc. in the body have been activated, however, it isdifficult to achieve sufficient antithrombogenicity without ananticoagulant therapy such as heparin administration.”

[0296] Other antithrombogenic methods and compositions are also wellknown. Thus, by way of further illustration, United States publishedpatent application 2001/0016611 discloses an antithrombogeniccomposition comprising an ionic complex of ammonium salts and heparin ora heparin derivative, said ammonium salts each comprising four aliphaticalkyl groups bonded thereto, wherein an ammonium salt comprising fouraliphatic alkyl groups having not less than 22 and not more than 26carbon atoms in total is contained in an amount of not less than 5% andnot more than 80% of the total ammonium salt by weight. The entiredisclosure of this published patent application is hereby incorporatedby reference into this specification.

[0297] Thus, e.g., U.S. Pat. No. 5,783,570 discloses an organicsolvent-soluble mucopolysaccharide consisting of an ionic complex of atleast one mucopolysaccharide (preferably heparin or heparin derivative)and a quaternary phosphonium, an antibacterial antithrombogeniccomposition comprising said organic solvent-soluble mucopolysaccharideand an antibacterial agent (preferably an inorganic antibacterial agentsuch as silver zeolite), and to a medical material comprising saidorganic solvent soluble mucopolysaccharide. The organic solvent-solublemucopolysaccharide, and the antibacterial antithrombogenic compositionand medical material containing same are said to easily impartantithrombogenicity and antibacterial property to a polymer to be a basematerial, which properties are maintained not only immediately afterpreparation of the material but also after long-term elution. The entiredisclosure of this United States patent is hereby incorporated byreference into this specification.

[0298] By way of further illustration, U.S. Pat. No. 5,049,393 disclosesanti-thrombogenic compositions, methods for their production andproducts made therefrom. The anti-thrombogenic compositions comprise apowderized anti-thrombogenic material homogeneously present in asolidifiable matrix material. The anti-thrombogenic material ispreferably carbon and more preferably graphite particles. The matrixmaterial is a silicon polymer, a urethane polymer or an acrylic polymer.The entire disclosure of this United States patent is herebyincorporated by reference into this specification.

[0299] By way of yet further illustration, U.S. Pat. No. 5,013,717discloses a leach resistant composition that includes a quaternaryammonium complex of heparin and a silicone. A method for applying acoating of the composition to a surface of a medical article is alsodisclosed in the patent. Medical articles having surfaces which are bothlubricious and antithrombogenic, are produced in accordance with themethod of the patent. The entire disclosure of this United States patentis hereby incorporated by reference into this specification.

[0300] Referring again to FIG. 35, and in the preferred embodimentdepicted therein, the sheath 4034 is non contiguous with the layer 4004;in this embodiment, another material 4036 (such as, e.g., air) ispresent. In FIG. 36, by comparison, the sheath 4034 is contiguous withthe layer 4004.

[0301] In both of the embodiments depicted in FIGS. 35 and 36, theconductor 4000 preferably has a resistivity at 20 degrees Centigrade offrom about 1 to about 100 nicro ohm-centimeters.

[0302] In one embodiment, not shown, the sheath 4034 is omitted and theshield 4004 itself is comprised of and/or acts as an antithrombogeniccomposition. In one aspect of this embodiment, the outer surface 4037 ofsheath 4034 is hydrophobic. In another aspect of this embodiment, theouter surface 4037 of the sheath is hydrophilic. Similarly, in theembodiments depicted in FIGS. 35 and 36, the outer surface 4037 of thesheath 4034 can be either hydrophobic or hydrophilic.

[0303] In this embodiment, the conductor assembly is comprised of amagnetic shield disposed above said flexible conductor, wherein saidmagnetic shield is comprised of an antithrombogenic composition, whereinsaid magnetic shield is comprised of a layer of magnetic shieldingmaterial, and wherein said layer of magnetic shielding material, whenexposed to a magnetic field with a intensity of at least about 30microTesla, has a magnetic shielding factor of at least about 0.5. Inone embodiment, the conductor assembly has a heat shielding factor of atleast about 0.2

[0304] A Process for Preparation of an Iron-Containing Thin Film

[0305] In one preferred embodiment of the invention, a sputteringtechnique is used to prepare an AlFe thin film as well as comparablethin films containing other atomic moieties, such as, e.g., elementalnitrogen, and elemental oxygen. Conventional sputtering techniques maybe used to prepare such films by sputtering. See, for example, R.Herrmann and G. Brauer, “D. C.—and R. F. Magnetron Sputtering,” in the“Handbook of Optical Properties: Volume I—Thin Films for OpticalCoatings,” edited by R. E. Hummel and K. H. Guenther (CRC Press, BocaRaton, Fla., 1955). Reference also may be had, e.g., to M. Allendorf,“Report of Coatings on Glass Technology Roadmap Workshop,” January18-19, 2000, Livermore, Calif.; and also to U.S. Pat. No. 6,342,134,“Method for producing piezoelectric films with rotating magnetronsputtering system.” The entire disclosure of each of these prior artdocuments is hereby incorporated by reference into this specification.

[0306] Although the sputtering technique is preferred, the plasmatechnique described elsewhere in this specification also may be used.

[0307] One may utilize conventional sputtering devices in this process.By way of illustration and not limitation, a typical sputtering systemis described in U.S. Pat. No. 5,178,739, the entire disclosure of whichis hereby incorporated by reference into this specification. As isdisclosed in this patent, “. . . a sputter system 10 includes a vacuumchamber 20, which contains a circular end sputter target 12, a hollow,cylindrical, thin, cathode magnetron target 14, a RF coil 16 and a chuck18, which holds a semiconductor substrate 19. The atmosphere inside thevacuum chamber 20 is controlled through channel 22 by a pump (notshown). The vacuum chamber 20 is cylindrical and has a series ofpermanent, magnets 24 positioned around the chamber and in closeproximity therewith to create a multipole field configuration near theinterior surface 15 of target 12. Magnets 26, 28 are placed above endsputter target 12 to also create a multipole field in proximity totarget 12. A singular magnet 26 is placed above the center of target 12with a plurality of other magnets 28 disposed in a circular formationaround magnet 26. For convenience, only two magnets 24 and 28 are shown.The configuration of target 12 with magnets 26, 28 comprises a magnetronsputter source 29 known in the prior art, such as the Torus-10E systemmanufactured by K. Lesker, Inc. A sputter power supply 30 (DC or RF) isconnected by a line 32 to the sputter target 12. A RF supply 34 providespower to RF coil 16 by a line 36 and through a matching network 37.Variable impedance 38 is connected in series with the cold end 17 ofcoil 16. A second sputter power supply 39 is connected by a line 40 tocylindrical sputter target 14. A bias power supply 42 (DC or RF) isconnected by a line 44 to chuck 18 in order to provide electrical biasto substrate 19 placed thereon, in a manner well known in the priorart.”

[0308] By way of yet further illustration, other conventional sputteringsystems and processes are described in U.S. Pat. No. 5,569,506 (amodified Kurt Lesker sputtering system); U.S. Pat. No. 5,824,761 (aLesker Torus 10 sputter cathode); U.S. Pat. No. 5,768,123; 5,645,910;6,046,398 (sputter deposition with a Kurt J. Lesker Co. Torus 2 sputtergun); U.S. Pat. No. 5,736,488; 5,567,673; 6,454,910; and the like. Theentire disclosure of each of these United States patents is herebyincorporated by reference into this specification.

[0309] By way of yet further illustration, one may use the techniquesdescribed in a paper by Xingwu Wang et al. entitled “Technique Devisedfor Sputtering AIN Thin Films,” published in “the Glass Researcher,”Volume 11, No. 2 (December 12, 2002). The entire disclosure of thispublication is hereby incorporated by reference into this specification.

[0310] In one preferred embodiment, a magnetron sputtering technique isutilized, with a Lesker Super System III system. The vacuum chamber ofthis system is cylindrical, with a diameter of approximately one meterand a height of approximately 0.6 meters. The base pressure used is fromabout 0.001 to 0.0001 Pascals. In one aspect of this process, the targetis a metallic FeAl disk, with a diameter of approximately 0.1 meter. Themolar ratio between iron and aluminum used in this aspect isapproximately 70/30. Thus, the starting composition in this aspect isalmost non-magnetic. See, e.g., page 83 (FIG. 3.laii) of R.S. Tebble etal.'s “Magnetic Materials” (Wiley-lnterscience, New York, N.Y., 1969);this Figure discloses that a bulk composition containing iron andaluminum with at least 30 mole percent of aluminum (by total moles ofiron and aluminum) is substantially non-magnetic.

[0311] In this aspect, to fabricate FeAl films, a DC power source isutilized, with a power level of from about 150 to about 550 watts(Advanced Energy Company of Colorado, model MDX Magnetron Drive). Thesputtering gas used in this aspect is argon, with a flow rate of fromabout 0.0012 to about 0.0018 standard cubic meters per second. Tofabricate FeAlN films in this aspect, in addition to the DC source, apulse-forming device is utilized, with a frequency of from about 50 toabout 250 MHz (Advanced Energy Company, model Sparc-le V). One mayfabricate FeAlO films in a similar manner but using oxygen rather thannitrogen.

[0312] In this aspect, a typical argon flow rate is from about (0.9 toabout 1.5)×10⁻³ standard cubic meters per second; a typical nitrogenflow rate is from about (0.9 to about 1.8)×10⁻³ standard cubic metersper second; and a typical oxygen flow rate is from about. (0.5 to about2)×10⁻³ standard cubic meters per second. During fabrication, thepressure typically is maintained at from about 0.2 to about 0.4 Pascals.Such a pressure range is found to be suitable for nanomagnetic materialsfabrications.

[0313] In this aspect, the substrate used may be either flat or curved.A typical flat substrate is a silicon wafer with or without a thermallygrown silicon dioxide layer, and its diameter is preferably from about0.1 to about 0.15 meters. A typical curved substrate is an aluminum rodor a stainless steel wire, with a length of from about 0.10 to about0.56 meters and a diameter of from (about 0.8 to about 3.0)×10⁻³ metersThe distance between the substrate and the target is preferably fromabout 0.05 to about 0.26 meters.

[0314] In this aspect, in order to deposit a film on a wafer, the waferis fixed on a substrate holder. The substrate may or may not be rotatedduring deposition. In one embodiment, to deposit a film on a rod orwire, the rod or wire is rotated at a rotational speed of from about0.01 to about 0.1 revolutions per second, and it is moved slowly backand forth along its symmetrical axis with a maximum speed of about 0.01meters per second.

[0315] In this aspect, to achieve a film deposition rate on the flatwafer of 5×10⁻¹⁰ meters per second, the power required for the FeAl filmis 200 watts, and the power required for the FeAlN film is 500 watts.The resistivity of the FeAlN film is approximately one order ofmagnitude larger than that of the metallic FeAl film. Similarly, theresistivity of the FeAlO filmis about one order of magnitude larger thanthat of the metallic FeAl film.

[0316] Iron containing magnetic materials, such as FeAl, FeAlN andFeAlO, have been fabricated by various techniques. The magneticproperties of those materials vary with stoichiometric ratios, particlesizes, and fabrication conditions; see, e.g., R.S. Tebble and D.J.Craik, “Magnetic Materials”, pp. 81-88, Wiley-lnterscience, New York,1969. As is disclosed in this reference, when the iron molar ratio inbulk FeAl materials is less than 70 percent or so, the materials will nolonger exhibit magnetic properties.

[0317] However, it has been discovered that, in contrast to bulkmaterials, a thin film material often exhibits different properties dueto the constraint provided by the substrate.

[0318] Nanomagnetic Compositions Comprised of Moieties A. B. and C

[0319] The aforementioned process described in the preceding section ofthis specification may be adapted to produce other, comparable thinfilms, as is illustrated in FIG. 37.

[0320] Referring to FIG. 37, and in the preferred embodiment depictedtherein, a phase diagram 5000 is presented. As is illustrated by thisphase diagram 5000, the nanomagnetic material used in the composition ofthis invention preferably is comprised of one or more of moieties A, B,and C.

[0321] The moiety A depicted in phase diagram 5000 is comprised of amagnetic element selected from the group consisting of a transitionseries metal, a rare earth series metal, or actinide metal, a mixturethereof, and/or an alloy thereof.

[0322] As is known to those skilled in the art, the transition seriesmetals include chromium, manganese, iron, cobalt, nickel. One may usealloys or iron, cobalt and nickel such as, e.g., iron—aluminum,iron—carbon, iron—chromium, iron—cobalt, iron—nickel, iron nitride(Fe₃N), iron phosphide, iron-silicon, iron-vanadium, nickel-cobalt,nickel-copper, and the like. One may use alloys of manganese such as,e.g., manganese-aluminum, manganese-bismuth, MnAs, MnSb, MnTe,manganese-copper, manganese-gold, manganese-nickel, manganese-sulfur andrelated compounds, manganese-antimony, manganese-tin, manganese-zinc,Heusler alloy, and the like. One may use compounds and alloys of theiron group, including oxides of the iron group, halides of the irongroup, borides of the transition elements, sulfides of the iron group,platinum and palladium with the iron group, chromium compounds, and thelike.

[0323] One may use a rare earth and/or actinide metal such as, e.g., Ce,Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, La, mixturesthereof, and alloys thereof. One may also use one or more of theactinides such as, e.g., Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md,No, Lr, Ac, and the like.

[0324] These moieties, compounds thereof, and alloys thereof are wellknown and are described, e.g., in the aforementioned text of R.S. Tebbleet al. entitled “Magnetic Materials.”

[0325] In one preferred embodiment, moiety A is selected from the groupconsisting of iron, nickel, cobalt, alloys thereof, and mixturesthereof. In this embodiment, the moiety A is magnetic, i.e., it has arelative magnetic permeability of from about 1 to about 500,000. As isknown to those skilled in the art, relative magnetic permeability is afactor, characteristic of a material, that is proportional to themagnetic induction produced in a material divided by the magnetic fieldstrength; it is a tensor when these quantities are not parallel. See,e.g., page 4-128 of E.U. Condon et al.'s “Handbook of Physics”(McGraw-Hill Book Company, Inc., New York, N.Y., 1958).

[0326] The moiety A also preferably has a saturation magnetization offrom about 1 to about 36,000 Gauss, and a coercive force of from about0.01 to about 5,000 Oersteds.

[0327] The moiety A may be present in the nanomagnetic material eitherin its elemental form, as an alloy, in a solid solution, or as acompound.

[0328] It is preferred at least about 1 mole percent of moiety A bepresent in the nanomagnetic material (by total moles of A, B, and C),and it is more preferred that at least 10 mole percent of such moiety Abe present in the nanomagnetic material (by total moles of A, B, and C).In one embodiment, at least 60 mole percent of such moiety A is presentin the nanomagnetic material, (by total moles of A, B, and C.)

[0329] In addition to moiety A, it is preferred to have moiety B bepresent in the nanomagnetic material. In this embodiment, moieties A andB are admixed with each other. The mixture may be a physical mixture, itmay be a solid solution, it may be comprised of an alloy of the A/Bmoieties, etc.

[0330] In one embodiment, the magnetic material A is dispersed withinnonmagnetic material B. This embodiment is depicted schematically inFIG. 38.

[0331] Referring to FIG. 38, and in the preferred embodiment depictedtherein, it will be seen that A moieties 5002, 5004, and 5006 areseparated from each other either at the atomic level and/or at thenanometer level. The A moieties may be, e.g., A atoms, clusters of Aatoms, A compounds, A solid solutions, etc; regardless of the form ofthe A moiety, it has the magnetic properties described hereinabove.

[0332] In the embodiment depicted in FIG. 38, each A moiety produces anindependent magnetic moment. The coherence length (L) between adjacent Amoieties is, on average, from about 0.1 to about 100 nanometers and,more preferably, from about 1 to about 50 nanometers.

[0333] Thus, referring again to FIG. 38, the normalized magneticinteraction between adjacent A moieties 5002 and 5004, and also between5004 and 5006, is preferably described by the formula M=exp(−x/L),wherein M is the normalized magnetic interaction, exp is the base of thenatural logarithm (and is approximately equal to 2.71828), x is thedistance between adjacent A moieties, and L is the coherence length.

[0334] In one embodiment, and referring again to FIG. 38, x ispreferably measured from the center 5001 of A moiety 5002 to the center5003 of A moiety 5004; and x is preferably equal to from about 0.00001 xL to about 100 x L.

[0335] In one embodiment, the ratio of x/L is at least 0.5 and,preferably, at least 1.5.

[0336] Referring again to FIG. 37, the nanomagnetic material may becomprised of 100 percent of moiety A, provided that such moiety A hasthe required normalized magnetic interaction (M). Alternatively, thenanomagnetic material may be comprised of both moiety A and moiety B.

[0337] When moiety B is present in the nanomagnetic material, inwhatever form or forms it is present, it is preferred that it be presentat a mole ratio (by total moles of A and B) of from about 1 to about 99percent and, preferably, from about 10 to about 90 percent.

[0338] The B moiety, in whatever form it is present, is nonmagnetic,i.e., it has a relative magnetic permeability of 1.0; without wishing tobe bound to any particular theory, applicants believe that the B moietyacts as buffer between adjacent A moieties. One may use, e.g., suchelements as silicon, aluminum, boron, platinum, tantalum, palladium,yttrium, zirconium, titanium, calcium, beryllium, barium, silver, gold,indium, lead, tin, antimony, germanium, gallium, tungsten, bismuth,strontium, magnesium, zinc, and the like.

[0339] In one embodiment, and without wishing to be bound to anyparticular theory, it is believed that B moiety provides plasticity tothe nanomagnetic material that it would not have but for the presence ofB. It is preferred that the bending radius of a substrate coated withboth A and B moieties be at least 110 percent as great as the bendingradius of a substrate coated with only the A moiety.

[0340] The use of the B material allows one to produce a coatedsubstrate with a springback angle of less than about 45 degrees. As isknown to those skilled in the art, all materials have a finite modulusof elasticity; thus, plastic deformations followed by some elasticrecovery when the load is removed. In bending, this recovery is calledspringback. See, e.g., page 462 of S. Kalparjian's “ManufacturingEngineering and Technology,” Third Edition (Addison Wesley PublishingCompany, New York, N.Y., 1995).

[0341]FIG. 39 illustrates how springback is determined in accordancewith this invention. Referring to FIG. 39, a coated substrate 5010 issubjected to a force in the direction of arrow 5012 that bends portion5014 of the substrate to an angle 5016 of 45 degrees, preferably in aperiod of less than about 10 seconds. Thereafter, when the force isreleased, the bent portion 5014 springs back to position 5018. Thespringback angle 5020 is preferably less than 45 degrees and,preferably, is less than about 10 degrees.

[0342] Referring again to FIG. 38, when an electromagnetic field 5022 isincident upon the nanomagnetic material 5026 comprised of A and B (seeFIG. 38), such a field will be reflected to some degree depending uponthe ratio of moiety A and moiety B. In one embodiment, it is preferredthat at least 1 percent of such field is reflected in the direction ofarrow 5024. In another embodiment, it is preferred that at least about10 percent of such field is reflected. In yet another embodiment, atleast about 90 percent of such field is reflected. Without wishing to bebound to any particular theory, applicants believe that the degree ofreflection depends upon the concentration of A in the A/B mixture.

[0343] M, the normalized magnetic interaction, preferably ranges fromabout 3×10−44 to about 1.0. In one preferred embodiment, M is from about0.01 to 0.99. In another preferred embodiment, M is from about 0.1 toabout 0.9.

[0344] Referring again to FIG. 37, and in one embodiment, thenanomagnetic material is comprised of moiety A, moiety C, and optionallymoiety B. The moiety C is preferably selected from the group consistingof elemental oxygen, elemental nitrogen, elemental carbon, elementalfluorine, elemental chlorine, elemental hydrogen, elemental helium,elemental neon, elemental argon, elemental krypton, elemental xenon, andthe like.

[0345] It is preferred, when the C moiety is present, that it be presentin a concentration of from about 1 to about 90 mole percent, based uponthe total number of moles of the A moiety and/or the B moiety and Cmoiety in the composition.

[0346] Referring again to FIG. 37, and in the embodiment depicted, thearea 5028 produces a composition which optimizes the degree to whichmagnetic flux are initially trapped and/or thereafter released by thecomposition when a magnetic field is withdrawing from the composition.

[0347] Without wishing to be bound to any particular theory, applicantsbelieve that, when a composition as described by area 5028 is subjectedto an alternating magnetic field, at least a portion of the magneticfield is trapped by the composition when the field is strong, and thenthis portion tends to be released when the field lessens in intensity.This theory is illustrated in FIG. 40.

[0348] Referring to FIG. 40, at time zero, the magnetic field 5022applied to the nanomagnetic material starts to increase, in a typicalsine wave fashion. After a specified period of time 5030, a magneticmoment is created within the nanomagnetic material; but, because of thetime delay, there is a phase shift.

[0349]FIG. 41 illustrates how a portion of the magnetic field 5022 istrapped within the nanomagnetic material and thereafter released.Referring to FIG. 41, it will be seen that the applied field 5022 istrapped after a time delay 5030 within the nanomagnetic material andthereafter, at point 5032, starts to release; at point 5034, the trappedflux is almost completely released.

[0350] The time delay 5030 (see FIGS. 40/41) will vary with thecomposition of the nanomagnetic material. By maximizing the amount oftrapping, and by minimizing the amount of reflection and absorption, onemay minimize the magnetic artifacts caused by the nanomagnetic shield.

[0351] Thus, one may optimize the A/B/C composition to preferably bewithin the area 5028 (see FIG. 37). In general, the A/B/C compositionhas molar ratios such that the ratio of A/(A and C) is from about 1 toabout 99 mole percent and, preferably, from about 10 to about 90 molepercent. In one preferred embodiment, such ratio is from about 40 toabout 60 molar percent.

[0352] The molar ratio of A/(A and B and C) generally is from about 1 toabout 99 mole percent and, preferably, from about 10 to about 90 molarpercent. In one embodiment, such molar ratio is from about 30 to about60 molar percent.

[0353] The molar ratio of B/(A plus B plus C) generally is from about 1to about 99 mole percent and, preferably, from about 10 to about 40 molepercent.

[0354] The molar ratio of C/(A plus B plus C) generally is from about 1to about 99 mole percent and, preferably, from about 10 to about 50 molepercent.

[0355] In one embodiment, the composition of the nanomagnetic materialis chosen so that the applied electromagnetic field 5022 is absorbed bythe nanomagnetic material by less than about 1 percent; thus, in thisembodiment, the applied magnetic field 5022 is substantially restored bycorrecting the time delay 5030. Referring to FIG. 41, and to theembodiment depicted, the applied magnetic field 5022 and the measuredmagnetic field 5023 are substantially identical, with the exception oftheir phases.

[0356] In another embodiment, illustrated in FIG. 42, the measured field5025 is substantially different from the applied field 5022. In thisembodiment, an artifact will be detected by the magnetic field measuringdevice (not shown). The presence of such an artifact, and its intensity,may be used to detect and quantify the exact location of the coatedsubstrate. In this embodiment, one preferably would use an area outsideof area 5028 (see FIG. 37), such as, e.g., area 5036.

[0357] In another embodiment, also illustrated in FIG. 42, the measuredfield 5025 has less intensity than the applied field 5022. One mayincrease the amount of absorption of the nanomagnetic material toproduce a measured field like measured field 5025 by utilizing the area5036 of FIG. 37.

[0358] By utilizing nanomagnetic material that absorbs theelectromagnetic field, one may selectively direct energy to variouscells that are to be treated. Thus, e.g., cancer cells can be injectedwith the nanomagnetic material and then destroyed by the application ofexternally applied electromagnetic fields. Because of the nano size ofapplicants' materials, they can readily and preferentially be directedto the malignant cells to be treated within a living organism. In thisembodiment, the nanomagnetic material preferably has a particle size offrom about 5 to about 10 nanometers and, thus, can be used in a mannersimilar to a tracer.

[0359] In one embodiment, the nanomagnetic material is injected into apatient's bloodstream. In another embodiment, the nanomagnetic materialis inhaled by a patient. In another embodiment, it is digested by apatient. In another embodiment, it is implanted through conventionalmeans. In each of these embodiments, conventional diagnostic means maybe utilized to determine when such material has reached to the targetsite(s), and then intense electromagnetic radiation may then be timelyapplied.

[0360] Example of the Preparation of a Nanomagnetic Material Coating

[0361] The following examples are presented to illustrate thepreparation of nanomagnetic material but are not to be deemed limitativethereof. Unless otherwise specified, all parts are by weight, and alltemperatures are in degrees Celsius.

[0362] In these examples, the fabrication of nanomagnetic materials wasaccomplished by a novel PVD sputtering process. A Kurt J. Lesker SuperSystem III deposition system outfitted with Lesker Torus 4 magnetronswas utilized; the devices were manufactured by the Kurt J. LekserCompany of Clairton, Pa.

[0363] The vacuum chamber of the system used in these examples wascylindrical, with a diameter of approximately one meter and a height ofabout 0.6 meters. The base pressure used was from 1 to 2 micro-torrs.

[0364] The target used was a metallic FeAl disk with a diameter of about0.1 meters. The molar ratio between the Fe and Al atoms was about 70/30.

[0365] In order to fabricate FeAl films, a direct current power sourceas utilized at a power level of from 150 to 550 watts; the power sourcewas an Advanced Energy MDX Magnetron Drive.

[0366] The sputtering gas used was argon, with a flow rate of from 15 to35 sccm.

[0367] In order to fabricate FeAlN films, a pulse system was added inseries with the DC power supply to provide pulsed DC. The magnetronpolarity switched from negative to positive at a frequency of 100kilohertz, and the pulse width for the positive or negative duration wasadjusted to yield suitable sputtering results (Advanced Energy Sparc-1eV).

[0368] In addition to using argon flowing at a rate of from 15 to 25sccm, nitrogen was supplied as a reactive gas with a flow rate of from15 to 30 sccm. During fabrication, the pressure was maintained at 24milli-torrs.

[0369] The substrate used was either a flat disk or a cylindrical rod. Atypical flat disk used was a silicon wafer with or without a thermallygrown silicon dioxide layer, with a diameter of from 0.1 to 0.15 meters.The thickness of the silicon dioxide layer was 50 nanometers. A typicalrod was an aluminum rod or a stainless steel wire with a length of from0.1 to 0.56 meters and a diameter of from 0.0008 to 0.003 meters.

[0370] The distance between the substrate and the target was from 0.05to 0.26 meters. To deposit a film on a wafer, the wafer was fixed on asubstrate holder, and there was no rotational motion. To deposit a filmon a rod of wire, the rod or wire was rotated at a speed of from 0.01 to0.1 revolutions per second and was moved slowly back and forth along itssymmetrical axis with the maximum speed being 0.01 meters per second.

[0371] A typical film thickness was between 100 nanometers and 1 micron,and a typical deposition time was between 200 and 2000 seconds. Theresistivity of an FelAI films was approximately 8×¹⁰⁻⁶ Ohm-meter. Theresistivity of an FeAlN film is approximately 200×10⁻⁶ Ohm-meter. Theresistivity of an FeAlO film was about 0.01 Ohm-meter.

[0372] The fabrication conditions used for FeAlO films was somewhatdifferent than those used for FeAl films. With the former films, thetarget was FeAlO, and the source was radio frequency with a power ofabout 900 watts.

[0373] Materials Characterization

[0374] According to surface profiler and SEM cross-sectionalmeasurements, the film thickness variation in a flat area of 0.13meters×0.13 meters was within 10 percent. As revealed by AFMmeasurement, the surface roughness of an FeAl film was about 3nanometers, and that of an FeAlN film was about 2 nanometers. All filmswere under compressive stress with the values for FeAl films under355×10⁶ Pascal, and those for FeAlN films under 675×10⁶ Pascal.

[0375] In order to determine the average chemical composition of a film,EDS was utilized to study the composition at four spots of the film,with a spot size of about 10 microns×10 microns×10 microns. For an FeAlfilm, the molar ratio of Fe/Al was about 39/61; and, for an FeAlN film,the molar ration of Fe/Al/N was about 19/25/56.

[0376] In each of the films, the Fe/Al ratio was different from that inthe target; and the relative iron concentration was lower than theeffective aluminum concentration.

[0377] The surface chemistry was studied via XPS. It was found that, onthe top surface of an FeAl film, within the top 10 nanometers, oxygenwas present in addition to Fe and Al; and the molar ratio of Fe/AI/O was17/13/70. It was found that, on the top surface of an FeAlN film oxygenwas also present in addition to Fe, Al, and N; and the molar ratio ofFe/Al/N/0 was 20/13/32/34.

[0378] In contrast to the average chemical composition of the films, onthe surface of the FeAl or FeAlN films, the relative iron concentrationwas higher than the relative aluminum concentration. To observe thevariations of the Fe/Al ratio below the top surface, SIMS was utilized.It was found that the relative Fe/Al ratio decreases as the distancefrom the top increases.

[0379] Both XRD and TEM were utilized to study the phase formation. FIG.43 illustrates the XRD pattern for an FeAl film. Besides broad amorphouspeaks, the major peak around 44 degrees coincides with the maindiffraction peaks of FeAl alloys, such as AlFe₃ (JCPDS Card number45-1203), and Al_(0.4)Fe_(0.6) (JCPDS Card number 45-0982). The averagecrystal size was estimated to be 7 nanometers by a computer programcalled “SHADOW” (S.A. Howard, “SHADOW: A system for X-ray powderdiffraction pattern analysis: Annotated program listings and tutorial,”University of Missouri-Rolla, 1990).

[0380] SEM analyses confirmed that both amorphous and crystalline phaseswere present in the films, and the sizes of the crystals were between 10nanometers and 30 nanometers.

[0381] The XRD pattern of an FeAlN film indicated that several broaddiffraction patterns are present, suggesting an amorphous growth. Thisamorphous growth was confirmed by TEM. For FeAlO films, as revealed byXRD and TEM, amorphous growth was the dominating mechanism.

[0382] Maqnetic Properties

[0383] For an FeAl film with a thickness of about 500 nanometers, thereal part of the relative permeability was about 40 in a direct currentfield and an alternating current field with a frequency lower than 200Megahertz, and the imaginary part of the permeability is nearly zero atfrequencies lower than 200 Megahertz. In FIG. 44, the real and imaginaryparts of the permeability were plotted as functions of frequency between200 Megahertz and 1.8 GHz. The value of the real part increases slightlyas the frequency increases, reaching a maximum value of 100 near 1.4GHz, and it decreases to zero near 1.7 GHz. The value of the imaginarypart reaches its maximum value at 1.6 GHz. Thus, the ferromagneticresonance frequency of the film is near 1.6 GHz. In FIG. 45, ahysteresis loop for the FeAl film is illustrated. The loop appeared tohave two sections. One section was in the region between plus and minus100 G, which has some squareness similar to that illustrated in FIG. 4for a thinner film. The other section was either was 100 G and 400 G, orbetween −100 G and −400 G, which may be indicating that the effectivemagnetic moment is approximately 0.046 emu, and the saturationmagnetization, 4πMs, is 9,120 Gauss. The effective anisotropy field isapproximately 400 G. For another FeAl film, with a thickness of about150 nanometers, a magnetic loop measured with VSM (at 300K) isillustrated in FIG. 46. The coercive force (Hc) was approximately 30Oersted, the remanence magnetic moment was about 0.0044 emu, and thesaturation magnetic moment was about 0.0056 emu. Thus, the squareness ofthe loop was about 80 percent. Correspondingly, the remanencemagnetization (4πMr) is about 2,908 G, and the saturation magnetization(4πMs) is about 3700 G. For an FeAlN film, with a thickness of about 414nanometers, a magnetic hysteresis loop measured with SQUID (at 5K) isillustrated in FIG. 47. The coercive force, Hc, is about 40 Oersted, theremanence magnetic moment was about 0.000008 emu, and the saturationmagnetic moment was about 0.000025 emu. Correspondingly, the remanencemagnetization was about 64 G, and the saturation magnetization was about2,000 G. The relative permeability was about 3.3. At 300 K, the value ofthe relative permeability is reduced to one, and the values of Hc, Mr,and Ms are also reduced.

[0384] For FeAlO films with thicknesses between 145 and 189 nanometers,the hysteresis loop of each film is similar to the FeAlN film. At 300 K,the relative permeability ranges from 0.28 to 3.3, Hc ranges from 20 to132 Oe, 4πMr ranges from 12 to 224 G, and 4πMs ranges from 800 to 1,640G. The ferromagnetic resonance frequency of an FeAlO film is about 9.5Gigahertz.

[0385]FIG. 48 is a schematic of a composite structure 5100 comprised ofa layer 5102 material that acts as a hermetic seal and/or isbiocompatible. The layer 5102 is disposed over insulator layer 5104;insulator layer 5104, in one embodiment, is not continuous.

[0386] The insulator layer 5104 is disposed over a layer 5106 ofnanomagnetic material; in one embodiment, nanomagnetic material layer5106 is not continuous. Layer 5106 is disposed over a layer 5108 ofinsulative material that, in turn, is disposed over conductor layer5110.

[0387] As will be apparent, the use of the insulating/dielectric layers5104 and 5104 together with the conductor layer 5110 has an effect uponthe capacitance of the structure 5100. Similarly, the use of the layer5106 of nanomagnetic material affects the inductance of the structure5100.

[0388] By varying the characteristics and the properties of theinsulator layers 5104/5108, and of the nanomagnetic material 5106, onecan, e.g., increase both the capacitance and the inductance of thesystem. In one embodiment, the inductance of system 5100 increasessubstantially, but the capacitance is not changed much.

[0389] A Novel Magnetic Resonance Imaging Assembly

[0390] In another embodiment of this invention, there is provided amagnetic resonance imaging assembly which utilizes an implanted medicaldevice that does not heat substantially during exposure to MRI radiationbut which, nonetheless, provides detectable feedback from suchradiation.

[0391] In one aspect of this embodiment, there is provided a magneticresonance imaging tracking assembly that comprises a medical devicecomprising a magnetic shield, means for generating a first highfrequency electromagnetic wave, means for sensing a modifiedhigh-frequency electromagnetic wave, means for producing an image fromsaid modified high-frequency electromagnetic wave, and means formodifying said image produced from said modified high-frequencyelectromagnetic wave.

[0392]FIG. 49 is a block diagram illustrating the components of atypical magnetic resonance imaging (MRI) unit 6000. This MRI unit 6000is comprised of means 6014 for producing certain types ofelectromagnetic radiation. Such radiation is generally comprised ofalternating electromagnetic waves with a frequency of at least about 21megahertz, depending on B₀.

[0393] MRI units with the capability of producing such electromagneticradiation are well known. Reference may be had, e.g., to U.S. Pat. No.4,733,189 (magnetic resonance imaging systems); U.S. Pat. No. 4,449,097(nuclear magnetic resonance systems); U.S. Pat. No. 5,867,027 (magneticresonance imaging apparatus); U.S. Pat. No. 5,568,051 (magneticresonance imaging apparatus having superimposed gradient coil); U.S.Pat. No. 5,329,232 (magnetic resonance methods and apparatus); and thelike. The entire disclosure of each of these United States patents ishereby incorporated by reference into this specification.

[0394] Referring again to FIG. 49, and in the preferred embodimentdepicted therein, it will be seen that MRI unit 6000 comprises animaging volume 6012 into which a patient or other sample to be imaged isplaced. In some MRI units, only a portion of the patient is placedwithin the imaging volume 6012 while the rest of the patient is outsidethe imaging volume 6012.

[0395] In many MRI units, the imaging volume 6012 is the space enclosedby one or more MRI coils. The patient is disposed within such space andimpacted over a 360-degree radius by radiation from such coils.

[0396] Thus, and referring again to FIG. 49 and to the embodimentdepicted therein, the MRI system 6000 preferably contains coils 6014that, in one embodiment, are usually comprised of a main coil (notshown) for generating a uniform magnetic field (not shown) through theimaging volume 6012. The coils 6014 also preferably comprise gradientcoils (not shown) to generate linear gradient magnetic variation in theimaging volume 6012, radio frequency transmit coils (not shown) fortransmitting a magnetic resonance excitation signal train, and one ormore pickup coils (not shown) to receive the de-excitation nuclearsignals from the imaging sample placed in the imaging volume 6012.Reference may be had, e.g., to U.S. Pat. No. 4,860,221 (magneticresonance imaging system), U.S. Pat. No. 5,184,074 (real-time MR imaginginside gantry room), U.S. Pat. No. 5,874,831 (magnetic resonance imagingsystem), U.S. Pat. No. 5,779,637 (magnetic resonance imaging systemincluding an image acquisition apparatus rotator), U.S. Pat. No.5,332,972 (gradient magnetic field generator for MRI system), and thelike. The entire disclosure of each of these United States patents ishereby incorporated by reference into this specification.

[0397] As will be apparent to those skilled in the art, one may utilizeother coils. In one embodiment, an imaging pickup coil(s) (not shown)which defines the imaging volume 6012 as the volume which the pickupcoil(s) (not shown) are sensitive to, is placed inside a patient.Reference may be had, e.g., to U.S. Pat. No. 5,476,095 (intracavityprobe and interface device for MRI imaging and spectroscopy); U.S. Pat.No. 5,451,232 (probe for MRI imaging and spectroscopy particularly inthe cervical region); U.S. Pat. No. 5,307,814 (externally moveableintracavity probe for MRI imaging and spectroscopy); U.S. Pat. No.6,263,229 (miniature magnetic resonance catheter coils and relatedmethods); U.S. Pat. No. 6,171,240 (MRI RF Catheter Coil); and the like.The entire disclosure of each of these United States patents is herebyincorporated by reference into this specification.

[0398] Referring again to FIG. 49, and to the preferred embodimentdepicted therein, the MRI unit 6000 preferably contains one or moreprogrammable logic units (PLU) 6016 for controlling the coils (6014). Inthe embodiment depicted, the PLU processes the received signals andcreates an image of an internal region (not shown) of the patient (notshown). See, e.g., the United States patents cited above as well as U.S.Pat. No. 6,445,182 (geometric distortion correction in magneticresonance imaging); U.S. Pat. No. 6,046,591 (MRI system with fractionaldecimation of acquired data); and U.S. Pat. No. 6,414,487 (time andmemory optimized method of acquiring and reconstructing multi-shotthree-dimensional MRI data). The entire disclosure of each of theseUnited States patents is hereby incorporated by reference into thisspecification.

[0399] Referring again to FIG. 49, an image is displayed onto a displayscreen 6020. This and other tasks of the PLU 6016 are controlled by thesoftware 6018 which the PLU executes.

[0400] In one embodiment, and referring again to FIG. 49, the software6018 is adapted to apply different signal filtering and image filteringalgorithms to the received signals. Thus, if some characteristic of thereceived signal is known to be caused by known material in the imagingvolume 6012, it is possible to enhance or eliminate the known materialfrom the displayed image. For example, bone will have a different MRIde-excitation signal than tissue. It is therefore possible to programthe software to enhance the tissue signal and the tissue image displayedto the physician while diminishing the signal from the bone material,thus diminishing or eliminating the bone image in the final displayedimage. This may be accomplished in part by filtering the receivedsignals.

[0401] Manipulation of the image data collected by an MRI system, aswell as the manipulation of the re-constructed image, is well known tothose skilled in the art. Reference may be had to U.S. Pat. No.6,459,922 (post data-acquisition method for generating water/fatseparated MR images having adjustable relaxation contrast). This patentdiscloses “A post data-acquisition magnetic resonance imaging (MRI)method is disclosed for generating water/fat separated MR images whereinthe resultant contrast in water-only or fat-only images is madeadjustable under operator control.” The entire disclosure of this UnitedStates patent is hereby incorporated by reference into thisspecification.

[0402] Reference may also be had to U.S. Pat. No. 5,909,119 (method andapparatus for providing separate fat and water MRI images in a singleacquisition scan) and U.S. Pat. No. 5,708,359 (interactive, stereoscopicmagnetic resonance imaging system). The U.S. Pat. No. 5,708,359 patentdiscloses further image manipulation, stating that: “Described are apreferred system and method for acquiring magnetic resonance signalswhich can be viewed stereoscopically in real or near-real time. Thepreferred stereoscopic MRI systems are interactive and allow for theadjustment of the acquired images in real time, for example to alter theviewing angle, contrast parameters, field of view, or positionassociated with the image, all advantageously facilitated byvoice-recognition software.” The entire disclosure of this United Statespatent is hereby incorporated by reference into this specification.

[0403] Reference also may be had to U.S. Pat. No. 6,175,655 (medicalimaging system for displaying, manipulating and analyzingthree-dimensional images). This patent discloses “A method and devicefor generating, displaying and manipulating three-dimensional images formedical applications is provided. The method creates a three-dimensionalimages from MRI or other similar medical imaging equipment. The medicalimaging system allows a user to view the three-dimensional model atarbitrary angles, vary the light or color of different elements, and toremove confusing elements or to select particular organs for closeviewing. Selection or removal of organs is accomplished using fuzzyconnectivity methods to select the organ based on morphologicalparameters.” The entire disclosure of this United States patent ishereby incorporated by reference into this specification.

[0404] Reference also may be had U.S. Pat. No. 6,486,671 (MRI imagequality improvement using matrix regularization); U.S. Pat. No.6,377,835 (method for separating arteries and veins in three-dimensionalMR angiographic images using correlation analysis); U.S. Pat. No.5,872,861 (digital image processing method for automatic detection ofstenoses); U.S. Pat. No. 6,345,112 (method for segmenting medical imagesand detecting surface anomalies in anatomical structures); U.S. Pat. No.6,426,994 (Image processing method); and U.S. Pat. No. 6,463,167(Adaptive filtering). The entire disclosure of each of these UnitedStates patents is hereby incorporated by reference into thisspecification.

[0405]FIG. 50 shows a cross section of a portion of a medical device6108 around which a magnetic shield 6114 is disposed. The medical device6108 in the embodiment depicted is preferably a catheter with a hollowlumen 6110 defined by a wall 6112. In another embodiment (not shown) themedical instrument is a catheter with multiple lumens. In anotherembodiment, not shown, the medical instrument 6108 is a stent withhollow lumen 6110 defined by a wall 6112. In another embodiment, notshown, the medical instrument 6108 is a biopsy needle with hollow lumen6110 defined by a wall 6112.

[0406] In the embodiment depicted in FIG. 50, a layer of shieldingmaterial 6114 is coated onto and is contiguous with the exteriorsurface/wall 6112 of the medical device 6110. In another embodiment, notshown in FIG. 50, the shielding material 6114 is disposed between thesource of electromagnetic radiation and the wall 6112 but is notnecessarily contiguous therewith. In this latter embodiment, e.g., alayer of insulating material, that does not act as a magnetic shield maybe disposed between the wall 6112 and the magnetic shield 6114.

[0407] In one embodiment, the magnetic shield 6114 is comprised of fromabout 10 to about 90 weight percent of nanomagnetic material withcertain specified properties. This type of material is disclosed inapplicants' U.S. Pat. No. 6,506,972, the entire disclosure of which ishereby incorporated by reference into this specification.

[0408] As is disclosed in U.S. Pat. No. 6,506,972, nanomagnetic materialis magnetic material which has an average particle size less than 100nanometers and, preferably, in the range of from about 2 to 50nanometers. Reference may be had, e.g., to U.S. Pat. No. 5,889,091(rotationally free nanomagnetic material); U.S. Pat. Nos. 5,714,136;5,667,924, and the like. The entire disclosure of each of these UnitedStates patents is hereby incorporated by reference into thisspecification.

[0409] Referring again to FIG. 50, it is preferred that the shield 6114provide a shielding efficiency of at least about 0.5 and, morepreferably, at least about 0.9. The shielding efficiency referred to iscalculated by measuring the magnetic field strength outside of theshield 6114 and the magnetic field strength within lumen 6110. Thedifference in these field strengths is the degree to which the shieldingis effective. This shielding effectiveness, when divided by the magneticfield strength outside of the shield 6114, is the shielding efficiency.

[0410]FIG. 51 is a schematic diagram illustrating a typical reaction ofa shielded medical device 6108 to MRI radiation. Referring to FIG. 51,and in the embodiment depicted therein, a known radio frequencyelectromagnetic wave 6150 that is transmitted from the MRI unit 6000(see FIG. 49) travels in the direction 6152. As will be apparent, and inthis embodiment, the electromagnetic radiation is in the form of a sinewave 6150.

[0411] Sine wave 6150 travels in the direction of arrow 6152 andcontacts shield 6114. In the embodiment depicted, sine wave 6150 is atleast somewhat modified by shield 6114. As used in this specification,the term modified refers to an electromagnetic wave that is partially ortotally absorbed and/or reflected and/or transmitted and/or phasechanged, and the like.

[0412] In the embodiment depicted in FIG. 51, the wave is partially ortotally reflected by shield 6114, to produce reflected wave 6154traveling in the direction of arrow 6156.

[0413] As will be apparent, a change in direction is only one of themeans in which incident wave 6150 is affected by shield 6114. As will beapparent from FIG. 51, the reflected wave 6154 has a wave shape thatdiffers from incident wave 6150, and the wavelength of wave 6154 differsfrom wave 6150.

[0414] As will be apparent to those skilled in the art, when the MRIassembly 6000 detects the shift in wavelength caused to incident wave6150, it can utilize its signal analyzing and filtering software(discussed elsewhere in this specification) to identify the reflectedwave signal and to also identify the properties of the substrate thatcaused such reflected wave signal. As will be apparent, each particularshielded device 6108 will have its own electronic signature and theeffect it has upon a specific MRI incident wave (or waves) can bedetermined.

[0415] One embodiment of the invention is disclosed in FIG. 52. Thus,e.g., and referring to FIG. 52, a known radio frequency electromagneticwave 6164 transmitted from the MRI unit 6000 of FIG. 49 in the direction6162 is incident upon the radio frequency electromagnetic wave modifyingmaterial coating 6114 of medical instrument 6108.

[0416] The incident electromagnetic wave 6164 is out of phase with thereflected wave 6168, not being coincident in time therewith; see howincident wave 6164 is reflected from the material 6114 as indicated bythe comparative markings labeled “X₀”, “X₁,”, “X₂”, “X₃”, and “X₄”. Thereflected wave 6168 is shown traveling in the opposite direction 6166 tothat of the incident wave 6164 direction 6162 only for convenience inillustrating the phase shift which occurs between the incident 6164 andreflected 6168 waves. In general, the reflected wave 6168 direction willnot be exactly opposite to the incident wave 6164 direction 6162.Knowing the reflected wave's characteristics, such as the phase shift ofthe incidence wave 6164 caused by the material coating 6114 allows thesoftware 6018 of FIG. 49 to be modified to either enhance or reduce thevisibility of the medical instrument 6108 in the image displayed to thephysician. In one embodiment, such image filtering is adjusted inreal-time by the physician who may wish to alternately have the medicalinstrument 6108 displayed and not displayed at various stages of amedical procedure.

[0417] In another embodiment (not shown) the radio frequency andgradient electromagnetic waves transmitted by the MRI system 6000 causesthe nuclei of the material coating (6114 of FIG. 50) to resonate and toproducing a nuclear resonance response signal detectable by the MRIsystem 6000. Such a nuclear resonance signal from the material 6114 isdistinct from any bio-material naturally occurring in a patient.

[0418]FIG. 53 is a schematic cross-sectional view of a portion of amedical device 6200 that comprises a magnetic shield material 6114disposed onto the surface of the wall 6112 of the device 6200. Themedical device 6200 in the embodiment depicted is preferably a catheterwith a hollow lumen 6110 defined by a wall 6112. A biologically inertcoating 6122 is applied over the magnetic shield material 6114.Biologically inert coating 6122 may be, e.g., Teflon, Tefzel or othermaterial. In one embodiment, the biologically inert coating 6122 is anantithrombogenic coating.

[0419]FIG. 54 is a schematic cross-sectional view of a portion of amedical device 6202 comprising a hollow lumen 6110 defined by walls6112. The walls 6112 are preferably coated with a bonding material 6203before the magnetic shield material 6114 is applied. Applying material6203 enhances the ability of the magnetic shield material 6114 to adhereto the medical device 6202. Material 6203 may be, e.g., a thin filmcoating of aluminum or other deposition of thin film material anddepends on the composition of the walls 6112 and the shield material6114. A biologically inert material 6122 is optionally applied to themagnetic shield material 6114.

[0420]FIG. 55 shows a cross section of a medical device 6204 comprisinga hollow lumen 6110 defined by the walls 6112. The walls 6112 are coatedwith an optional bonding material 6203. Magnetic shield material 6114 isapplied over the bonding material 6203.

[0421] In another embodiment (not shown, but refer to FIG. 50) themagnetic shield material is applied directly to wall 6112.

[0422] Continuing to refer to FIG. 55 and to the embodiment depictedtherein, a second magnetic shield material 6205 is applied over themagnetic shield material 6114. In one embodiment the magnetic shieldmaterial 6205 has a different composition than that of magnetic shieldmaterial 6114.

[0423] Continuing to refer to FIG. 55, an optional outer biologicallyinert coating 6122 is applied to magnetic shield material 6205.

[0424]FIGS. 56A through 56C illustrate one preferred process of theinvention. As is illustrated in FIG. 56A, a biological organism 7002 isshown being irradiated with electromagnetic radiation 7000 in a magneticresonance (MR) imaging process. As a result of this irradiation, asignal 7004 that represents an undistorted image of the organism 7002 isproduced; and, from this signal 7004, a displayed image 7006 isgenerated. This displayed image 7006 is representative of the true stateof the biological organism; it contains no significant artifacts.

[0425] By comparison, and in the situation depicted in FIG. 56B, thebiological organism 7002 contains disposed within it a medical device7008. In this situation, when organism 7002 is irradiated with the MRradiation 7000, a different signal 7005 is produced; and an image ofthis different, distorted signal is presented in display 7006. Due tothe interference caused by the medical device 7008, the image 7010 isnot representative of the true state of either the biological organism7002 or of the medical device 7008. It is said that the image 7010 isdistorted by substantial image artifacts.

[0426]FIG. 56C represents the situation that occurs when the implantedmedical device 7008 is coated with a nanomagnetic coating of thisinvention. In this case, because the “signature” of the coated medicaldevice differs from the “signature” of the uncoated medical device, theimage 7012 is less distorted by substantial image artifacts than is theimage 7010; and, by proper choice of properties of the nanomagneticcoating, the image 7012 is representative of the true state of thebiological organism 7002 and of the device 7008. The relative accuracyof this image 7012 is due to the fact that any interference due tomedical device 7008 is mitigated by the presence of coating 7014.

[0427] To correct this problem, one may image medical device 7014 by MRradiation 7000 ex vivo, outside of the biological organism 7002. Withdata obtained from such imaging, the MRI may then be calibrated suchthat a correct waveform is generated that compensates for the presenceof the device 7014. This calibration may be conducted in accordance withthe formula D=f [(M)e^(ia)], wherein D is the distortion, f indicatesthe variables that D is a function of, M is the magnitude of theelectromagnetic wave, e is the natural logarithm base, i is the squareroot of −1, and a is a phase factor that is equal to the phase of theelectromagnetic wave that is detected and displayed in the display 7006.

[0428] As is disclosed elsewhere in this specification, by theappropriate choice of materials for the nanomagnetic coating 7012, onemay adjust the phase factor a so that D, as corrected, is equal to 1.

[0429] Some of the image artifact problems caused by implanted medicaldevices during MRI imaging are illustrated and discussed in a book byFrank G. Shellock entitled “Magnetic Resonance Procedures: HealthEffects and Safety” (CRC Press, LLC, Boca Raton, Fla., 2001).

[0430]FIG. 14.4(a) of this Shellock book (at page 281) illustratesintracranial aneurysm clips, some of which contain ferromagneticmaterials and, thus, are contraindicated for patients undergoingconventional MR procedures. FIG. 14.4(b) of the Shellock bookillustrates the image artifacts caused by these aneurysm clips. It wasnoted by the author that “. . . the smallest artifacts are seen for theaneurysm clips made from titanium alloy and commercially pure titanium.”

[0431] Similarly, FIG. 14.14 of the Shellock book (see page 298)illustrates a “T1−weighted, coronal plane image of the hips and pelvisobtained from a patient with a contraceptive diaphragm in place.” Theauthor urged the readers to “Note the presence of the substantialartifacts and image distortion.”

[0432] As will be apparent, the process of this invention, when appliedto these and other medical devices, resolves the prior art distortionproblem.

[0433] In one embodiment, the radio-frequency wave produced during MRIimaging is a pulsed electromagnetic wave with a pulse duration of fromabout 1 microsecond to about 100 nilliseconds. As is disclosed on page70 of a book by Zhi-Pei Liang et al. entitled “Principels of MagneticResonance Imaging (IEEE Press, New York, N.Y., 2000), “RF pulse is asynonym of the B₁ field so called because the B₁ field is short-livedand oscillates in the radio-frequency range. Specifically, the B₁ fieldis normally turned on for a few microseconds or milliseconds . . . theB₁ field is much weaker (e.g., B₁=50 mT . . . ).”

[0434] In one embodiment, the pulsed RF electromagnetic wave producedduring MR imaging has a repetition rate of from about 10 to about 50,000milliseconds. In one aspect of this embodiment, the amplitude of suchpulsed RF electromagnetic wave is from about 10 microTesla to about 100nilliTesla.

[0435] The switched gradient magnetic field present during MRI imagingpreferably has a rise time up to its maximum amplitude of from about 0.1to about 2 milliseconds as the field strength rises from 0 to 10milliTesla per meter.

[0436] Although the invention has been shown and described with respectto a preferred embodiment thereof, it should be understood by thoseskilled in the art that various changes and omissions in the form anddetail thereof may be made therein without departing from the spirit andscope of the invention.

I claim:
 1. A magnetic resonance imaging tracking assembly thatcomprises a medical device having a magnetic shield comprised of a layerof nanomagnetic material, means for contacting said magnetic shield witha first high frequency electromagnetic wave, means for modifying saidfirst high frequency electromagnetic wave with said magnetic shield toproduce a second high frequency electromagnetic wave, and means fortransmitting said second high frequency electromagnetic wave from saidlayer of nanomagnetic material, wherein: a. said medical device isdisposed within a biological organism, b. said nanomagnetic material hasan average particle size of less than about 1000 nanometers, c. saidlayer of nanomagnetic material has a saturation magnetization of fromabout 200 to about 26,000 Gauss, d. said layer of nanomagnetic materialis disposed between said first high frequency electromagnetic wave andsaid medical device, e. said layer of nanomagnetic material has athickness of less than about 2 microns, f. said first high frequencyelectromagnetic wave has a frequency of from at least 21 megahertz toabout 128 megahertz.
 2. A magnetic resonance imaging tracking assemblythat comprises a medical device having a magnetic shield, means forcontacting said magnetic shield with a first electromagnetic wave, meansfor modifying said first electromagnetic wave with said magnetic shieldto produce a second electromagnetic wave, and means for sensing saidsecond electromagnetic wave wherein: a. said medical device is disposedwith a biological organism, b. said magnetic shield is comprised of alayer of said nanomagnetic material, wherein: i. said layer ofnanomagnetic material is disposed between said first electromagneticwave and said medical device, ii. said nanomagnetic material has anaverage particle size of less than about 100 nanometers, and iii. saidlayer of nanomagnetic material has a saturation magnetization of fromabout 200 to about 26,000 Gauss and a thickness of less than about 10microns.
 3. A magnetic resonance imaging tracking assembly as recited inclaim 2, wherein said first electromagnetic wave is a pulsed frequencyelectromagnetic wave.
 4. A magnetic resonance imaging tracking assemblyas recited in claim 3, wherein said pulsed frequency electromagneticwave has a pulse duration of from about 1 microsecond to about 100milliseconds.
 5. A magnetic resonance imaging tracking assembly asrecited in claim 2, wherein said medical device is comprised of aconductor.
 6. A magnetic resonance imaging tracking assembly as recitedin claim 5, wherein said conductor is flexible, having a bend radius ofless than 2 centimeters.
 7. A magnetic resonance imaging trackingassembly that comprises a medical device having a magnetic shieldcomprised of nanomagnetic material, means for contacting said magneticshield with a first electromagnetic wave, means for modifying said firstelectromagnetic wave to produce a second electromagnetic wave, and meansfor transmitting said second electromagnetic wave from the nanomagneticmaterial, wherein: a. said layer of nanomagnetic material has asaturation magnetization of from about 200 to about 26,000 Gauss, b.said first electromagnetic wave has a frequency of from at least about21 megahertz to about 128 megahertz, c. said nanomagnetic particles areat least triatomic, being comprised of a first distinct atom, a seconddistinct atom, and a third distinct atom.
 8. A magnetic resonanceimaging tracking assembly as recited in claim 7, further comprisingmeans for sensing said second electromagnetic wave.
 9. A magneticresonance imaging tracking assembly as recited in claim 8, furthercomprising means for producing an image from said second electromagneticwave.
 10. A magnetic resonance imaging tracking assembly as recited inclaim 9, wherein said first wave is a pulsed electromagnetic wave.
 11. Amagnetic resonance imaging tracking assembly as recited in claim 7,wherein said first distinct atom selected from the group consisting ofiron, nickel, and cobalt.
 12. A magnetic resonance imaging trackingassembly as recited in claim 11, wherein said second distinct atom isselected from the group consisting of silicon, aluminum, boron,platinum, tantalum, palladium, yttrium, zirconium, titanium, calcium,beryllium, barium, silver, gold, indium, lead, tin, antimony, germanium,gallium, tungsten, bismuth, strontium, magnesium, and zinc.
 13. Amagnetic resonance imaging tracking assembly as recited in claim 12,wherein said third distinct atom is selected from the group consistingof oxygen, nitrogen, carbon, fluorine, chlorine, hydrogen, helium, neon,argon, krypton, and xenon.
 14. A magnetic resonance imaging trackingassembly as recited in claim 7, wherein said first distinct atom isiron.
 15. A magnetic resonance imaging tracking assembly as recited inclaim 14, wherein said second distinct atom is aluminum.
 16. A magneticresonance imaging tracking assembly as recited in claim 15, wherein saidthird distinct atom is nitrogen.
 17. A magnetic resonance imagingtracking assembly as recited in claim 15, wherein said nanomagneticparticles are further comprised of a fourth distinct atom.
 18. Amagnetic resonance imaging tracking assembly as recited in claim 17,wherein said fourth distinct atom is oxygen.
 19. A magnetic resonanceimaging tracking assembly as recited in claim 14, further comprisingmeans for producing said first electromagnetic wave.
 20. A magneticresonance imaging tracking assembly as recited in claim 14, furthercomprising means for cooling said medical device.